By user456584

2011-11-29 22:54:22 8 Comments

How come certain random strings produce colors when entered as background colors in HTML? For example:

<body bgcolor="chucknorris"> test </body>

...produces a document with a red background across all browsers and platforms.

Interestingly, while chucknorri produces a red background as well, chucknorr produces a yellow background.

What's going on here?


@Alireza 2017-07-01 04:08:59

The reason is the browser can not understand it and try to somehow translate it to what it can understand and in this case into a hexadecimal value!...

chucknorris starts with c which is recognised character in hexadecimal, also it's converting all unrecognised characters into 0!

So chucknorris in hexadecimal format becomes: c00c00000000, all other characters become 0 and c remains where they are...

Now they get divided by 3 for RGB(red, green, blue)... R: c00c, G: 0000, B:0000...

But we know valid hexadecimal for RGB is just 2 characters, means R: c0, G: 00, B:00

So the real result is:


I also added the steps in the image as a quick reference for you:

Why does HTML think “chucknorris” is a colour?

@Dominik Bucher 2019-06-09 21:02:13

This is so cute explanation :D :D :D

@Saurin Vala 2020-02-12 13:21:02

So wise and very simple and straigh forward explanation I have ever experienced

@ahmednawazbutt 2020-02-13 08:27:44

very creative answer :)

@Squ1rr3lz 2020-08-23 19:50:51

Best and most creative answer I've seen on any topic.

@sameera lakshitha 2018-04-17 19:16:30

chucknorris starts with c, and the browser reads it into a hexadecimal value.

Because A, B, C, D, E, and F are characters in hexadecimal.

The browser converts chucknorris to a hexadecimal value, C00C00000000.

Then the C00C00000000 hexadecimal value is converted to RGB format (divided by 3):

C00C00000000 => R:C00C, G:0000, B:0000

The browser needs only two digits to indicate the colour:

R:C00C, G:0000, B:0000 => R:C0, G:00, B:00 => C00000

Finally, show bgcolor = C00000 in the web browser.

Here's an example demonstrating it:

    <td bgcolor="chucknorris" cellpadding="10" width="150" align="center">chucknorris</td>
    <td bgcolor="c00c00000000" cellpadding="10" width="150" align="center">c00c00000000</td>
    <td bgcolor="c00000" cellpadding="10" width="150" align="center">c00000</td>

@Salman A 2018-10-17 14:53:02

The rules for parsing colors on legacy attributes involves additional steps than those mentioned in existing answers. The truncate component to 2 digits part is described as:

  1. Discard all characters except the last 8
  2. Discard leading zeros one by one as long as all components have a leading zero
  3. Discard all characters except the first 2

Some examples:

000F 000F 000F                <- replace, pad and chunk
0F 0F 0F                      <- leading zeros truncated
0F 0F 0F                      <- truncated to 2 characters from right

000F 00FF 0FFF                <- replace, pad and chunk
00F 0FF FFF                   <- leading zeros truncated
00 0F FF                      <- truncated to 2 characters from right

ABC000000 ABC000000 ABC000000 <- replace, pad and chunk
BC000000 BC000000 BC000000    <- truncated to 8 characters from left
BC BC BC                      <- truncated to 2 characters from right

A0C000000 A0C000000 A0C000000 <- replace, pad and chunk
0C000000 0C000000 0C000000    <- truncated to 8 characters from left
C000000 C000000 C000000       <- leading zeros truncated
C0 C0 C0                      <- truncated to 2 characters from right

Below is a partial implementation of the algorithm. It does not handle errors or cases where the user enters a valid color.

function parseColor(input) {
  // todo: return error if input is ""
  input = input.trim();
  // todo: return error if input is "transparent"
  // todo: return corresponding #rrggbb if input is a named color
  // todo: return #rrggbb if input matches #rgb
  // todo: replace unicode code points greater than U+FFFF with 00
  if (input.length > 128) {
    input = input.slice(0, 128);
  if (input.charAt(0) === "#") {
    input = input.slice(1);
  input = input.replace(/[^0-9A-Fa-f]/g, "0");
  while (input.length === 0 || input.length % 3 > 0) {
    input += "0";
  var r = input.slice(0, input.length / 3);
  var g = input.slice(input.length / 3, input.length * 2 / 3);
  var b = input.slice(input.length * 2 / 3);
  if (r.length > 8) {
    r = r.slice(-8);
    g = g.slice(-8);
    b = b.slice(-8);
  while (r.length > 2 && r.charAt(0) === "0" && g.charAt(0) === "0" && b.charAt(0) === "0") {
    r = r.slice(1);
    g = g.slice(1);
    b = b.slice(1);
  if (r.length > 2) {
    r = r.slice(0, 2);
    g = g.slice(0, 2);
    b = b.slice(0, 2);
  return "#" + r.padStart(2, "0") + g.padStart(2, "0") + b.padStart(2, "0");

$(function() {
  $("#input").on("change", function() {
    var input = $(this).val();
    var color = parseColor(input);
    var $cells = $("#result tbody td");
    $cells.eq(0).attr("bgcolor", input);
    $cells.eq(1).attr("bgcolor", color);

    var color1 = $cells.eq(0).css("background-color");
    var color2 = $cells.eq(1).css("background-color");
    $cells.eq(2).empty().append("bgcolor: " + input, "<br>", "getComputedStyle: " + color1);
    $cells.eq(3).empty().append("bgcolor: " + color, "<br>", "getComputedStyle: " + color2);
body { font: medium monospace; }
input { width: 20em; }
table { table-layout: fixed; width: 100%; }
<script src=""></script>

<p><input id="input" placeholder="Enter color e.g. chucknorris"></p>
<table id="result">
      <th>Left Color</th>
      <th>Right Color</th>

@aWebDeveloper 2013-11-30 14:05:38

The browser is trying to convert chucknorris into hex colour code, because it's not a valid value.

  1. In chucknorris, everything except c is not a valid hex value.
  2. So it gets converted to c00c00000000.
  3. Which becomes #c00000, a shade of red.

This seems to be an issue primarily with Internet Explorer and Opera (12) as both Chrome (31) and Firefox (26) just ignore this.

P.S. The numbers in brackets are the browser versions I tested on.


On a lighter note

Chuck Norris doesn't conform to web standards. Web standards conform to him. #BADA55

@Webeng 2016-05-24 05:18:14


  • The browser will try to convert chucknorris into a hexadecimal value.
  • Since c is the only valid hex character in chucknorris, the value turns into: c00c00000000(0 for all values that were invalid).
  • The browser then divides the result into 3 groupds: Red = c00c, Green = 0000, Blue = 0000.
  • Since valid hex values for html backgrounds only contain 2 digits for each color type (r, g, b), the last 2 digits are truncated from each group, leaving an rgb value of c00000 which is a brick-reddish toned color.

@Jeremy Goodell 2012-10-17 17:55:48

I'm sorry to disagree, but according to the rules for parsing a legacy color value posted by @Yuhong Bao, chucknorris DOES NOT equate to #CC0000, but rather to #C00000, a very similar but slightly different hue of red. I used the Firefox ColorZilla add-on to verify this.

The rules state:

  • make the string a length that is a multiple of 3 by adding 0s: chucknorris0
  • separate the string into 3 equal length strings: chuc knor ris0
  • truncate each string to 2 characters: ch kn ri
  • keep the hex values, and add 0's where necessary: C0 00 00

I was able to use these rules to correctly interpret the following strings:

  • LuckyCharms
  • Luck
  • LuckBeALady
  • LuckBeALadyTonight
  • GangnamStyle

UPDATE: The original answerers who said the color was #CC0000 have since edited their answers to include the correction.

@Jeremy Goodell 2012-10-17 18:11:21

I figured it out, I had misinterpreted some of the parsing instructions: "adamlevine" = "ada00e000e" = "ada00e000e00" = "ada0 0e00 0e00" = "ad 0e 0e" -- Perfect!!

@Jeremy Goodell 2012-10-17 18:50:28

In case you're interested, I posted the 5-step algorithm as an UPDATE on a similar question I posted today:…

@Jeremy Goodell 2014-02-06 19:01:38

@TimPietrusky created this freaking incredible demo tool for random color names. Just go here: and click in the box and type "chucknorris".

@Martin 2016-01-26 22:26:26

adamlevine does work as per but the letters are blocked into ada00e000e which is padded to ada00e000e00 but then reduced down to the typical HEX 6 digit value of [ad]a0[0e]00[0e]00 thus making ad0e0e which appears in the jsfiddle above.

@Peter Mortensen 2016-01-31 12:13:22

It would be better if this answer only contained the current state - the history of this answer and other answers belongs in the edit summaries and/or comments.

@Richard Hunter 2020-09-19 18:50:14

Good to point out errors, but once the original post is corrected you should just delete this.

@Yuhong Bao 2012-09-27 22:01:58

The WHATWG HTML spec has the exact algorithm for parsing a legacy color value:

The code Netscape Classic used for parsing color strings is open source:

For example, notice that each character is parsed as a hex digit and then is shifted into a 32-bit integer without checking for overflow. Only eight hex digits fit into a 32-bit integer, which is why only the last 8 characters are considered. After parsing the hex digits into 32-bit integers, they are then truncated into 8-bit integers by dividing them by 16 until they fit into 8-bit, which is why leading zeros are ignored.

Update: this code does not exactly match what is defined in the spec, but the only difference there is a few lines of code. I think it is these lines that was added (in Netscape 4):

if (bytes_per_val > 4)
      bytes_per_val = 4;

@kb1000 2020-03-18 08:11:29

Thanks, you showed me where the old Netscape source code is... why is it so hard to find?

@dash 2011-11-30 21:53:38

It's a holdover from the Netscape days:

Missing digits are treated as 0[...]. An incorrect digit is simply interpreted as 0. For example the values #F0F0F0, F0F0F0, F0F0F, #FxFxFx and FxFxFx are all the same.

It is from the blog post A little rant about Microsoft Internet Explorer's color parsing which covers it in great detail, including varying lengths of color values, etc.

If we apply the rules in turn from the blog post, we get the following:

  1. Replace all nonvalid hexadecimal characters with 0's

    chucknorris becomes c00c0000000
  2. Pad out to the next total number of characters divisible by 3 (11 -> 12)

    c00c 0000 0000
  3. Split into three equal groups, with each component representing the corresponding colour component of an RGB colour:

    RGB (c00c, 0000, 0000)
  4. Truncate each of the arguments from the right down to two characters

Which gives the following result:

RGB (c0, 00, 00) = #C00000 or RGB(192, 0, 0)

Here's an example demonstrating the bgcolor attribute in action, to produce this "amazing" colour swatch:

    <td bgcolor="chucknorris" cellpadding="8" width="100" align="center">chuck norris</td>
    <td bgcolor="mrt"         cellpadding="8" width="100" align="center" style="color:#ffffff">Mr T</td>
    <td bgcolor="ninjaturtle" cellpadding="8" width="100" align="center" style="color:#ffffff">ninjaturtle</td>
    <td bgcolor="sick"  cellpadding="8" width="100" align="center">sick</td>
    <td bgcolor="crap"  cellpadding="8" width="100" align="center">crap</td>
    <td bgcolor="grass" cellpadding="8" width="100" align="center">grass</td>

This also answers the other part of the question; why does bgcolor="chucknorr" produce a yellow colour? Well, if we apply the rules, the string is:

c00c00000 => c00 c00 000 => c0 c0 00 [RGB(192, 192, 0)]

Which gives a light yellow gold colour. As the string starts off as 9 characters, we keep the second C this time around hence it ends up in the final colour value.

I originally encountered this when someone pointed out you could do color="crap" and, well, it comes out brown.

@Aaron Dufour 2013-02-05 20:32:22

Note that, despite what that blog post says, when you get to handling 3-char strings, you duplicate each character, rather than prepending 0. i.e. 0F6 becomes #00FF66, not #000F06.

@Lily Ballard 2013-02-05 23:43:02

@usr: HTML is built around intentionally ignoring malformed input ;)

@TimPietrusky 2013-03-11 16:45:17

You can also use my random string to css color converter to get the color for a specific string. It's based on the 5 steps to calculate the string color by Jeremy Goodell.

@Theraot 2013-12-16 22:47:35

A hidden opportunity for semantics? You could make some error pages with this: <body bgcolor=error><h1 style=text-align:center>Error: Not Found<h1></span> You could add a div with anothe background or something like that, so it is not that aesthetically shocking.

@phuclv 2014-08-07 05:40:06

Why do it truncate from the right instead of keeping the low significant digits like normal arithmatics in computers do?

@3Doubloons 2014-09-15 04:15:46

@LưuVĩnhPhúc Because this way preserves the colour ratio. Ultimately, you'll convert your colour to a percentage of the maximum value: if you're trying to convert f05 in one of your channels, 0xf0 / 0xff is a lot closer than 0x05/0xff to 0xf05 / 0xfff

@daiscog 2016-03-01 12:39:17

@Theraot bgcolor="success" is a nice green, too. Interestingly, one can override these colours using CSS attribute/value selectors (e.g., td[bgcolor="chucknorris"] {...}).

@Nyerguds 2016-12-22 13:42:18

@AaronDufour that is actually logical; the most accurate representation of 6 on a scale of F when converted to a scale of FF is indeed 66. If you don't do that, the higher the value is, the more it'll deviate from the intended colour: FFF, which is meant to be white, should become FFFFFF, not F0F0F0. I encountered this problem when generating 16-colour gradient palettes.

@tvanc 2017-01-20 17:11:00

@TimPietrusky I get a different results in Chrome and your converter when I plug in the name "veronica"

@SDsolar 2017-06-03 18:54:44

I tip my hat to you, @dash. Amazing explanation. I was leaning towards #9 in this list:…

@BoltClock 2018-02-07 05:30:56

@Theraot: Too bad bgcolor is a presentational attribute and therefore carries zero semantic value, making it functionally equivalent to class="error" while being invalid, and 2 bytes longer.

@BoltClock 2018-02-07 05:33:52

@Dave Everitt: I left a similar anecdote here many years ago (which I allude to in a comment on the question) and it got flagged and deleted - twice. C'est la vie.

@Thomas Mulder 2018-05-14 13:37:52

@TimPietrusky chucknorr like in OP's question doesn't output the expected yellowish rgb(192, 192, 0)

@Mikko Rantalainen 2018-09-05 07:27:01

You're missing the rules to correctly compute <body bgcolor="dog💩">:…

@Gaurav Singh 2019-07-01 09:49:25

@DaveEveritt At the risk of getting downvoted, W3Schools editor is your friend (atleast for this purpose).

@Nick.McDermaid 2020-02-16 09:30:41

Chuck Norris doesn't need HTML rules he makes his own.

@Mike Christensen 2011-11-29 23:01:05

Most browsers will simply ignore any NON-hex values in your color string, substituting non-hex digits with zeros.

ChuCknorris translates to c00c0000000. At this point, the browser will divide the string into three equal sections, indicating Red, Green and Blue values: c00c 0000 0000. Extra bits in each section will be ignored, which makes the final result #c00000 which is a reddish color.

Note, this does not apply to CSS color parsing, which follow the CSS standard.

<p><font color='chucknorris'>Redish</font></p>
<p><font color='#c00000'>Same as above</font></p>
<p><span style="color: chucknorris">Black</span></p>

@Mike Christensen 2011-11-29 23:19:12

Though I'm still curious as to why OP said "in CSS" and not "in HTML" - Maybe they're using a super old browser, or just mistaken?

@animuson 2011-11-29 23:20:15

So then he is more than likely using the deprecated bgcolor attribute.

@treat your mods well 2012-09-28 03:30:30

Invalid characters are not skipped, they are treated as 0.

@Zoe 2017-06-07 11:37:08

(WHile this answer may be dead) suggestion: Use background color instead to demonstrate teh colors. Text color is over such a small relative area it is hard to see differences or similarities

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