Why do certain random strings produce colors when entered as background colors in HTML?
For example, bgcolor="chucknorris" produces a red background:
<body bgcolor="chucknorris"> test </body>Conversely, bgcolor="chucknorr" produces a yellow background:
<body bgcolor="chucknorr"> test </body>This holds true across various browsers and platforms. What’s going on here?
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:
Replace all nonvalid hexadecimal characters with 0’s:
chucknorris becomes c00c0000000
Pad out to the next total number of characters divisible by 3 (11 → 12):
c00c 0000 0000
Split into three equal groups, with each component representing the corresponding colour component of an RGB colour:
RGB (c00c, 0000, 0000)
Truncate each of the arguments from the right down to two characters.
Which, finally, 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:
<table>
<tr>
<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>
</tr>
<tr>
<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>
</tr>
</table>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 that you could do color="crap" and, well, it comes out brown.
Charmeleon, Ivysaur, and Squirtle will produce red, green, and blue colors respectively.
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:
chucknorris0chuc knor ris0ch kn riC0 00 00I was able to use these rules to correctly interpret the following strings:
LuckyCharmsLuckLuckBeALadyLuckBeALadyTonightGangnamStyleThe original answerers who said the color was #CC0000 have since edited their answers to include the correction.
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:
bgcolor="#c00000";
I also added the steps in the image as a quick reference for you:
Most browsers will simply ignore any non-hexadecimal values in your color string, substituting non-hexadecimal 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>
You might consider editing your answer, because the <font> element is hereby obsolete by HTML5.
Commented
May 8, 2021 at 20:53
The browser is trying to convert chucknorris into a hexadecimal color code because it’s not a valid value.
chucknorris, everything except c is not a valid hexadecimal value.c00c00000000.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.
Similarly, Rajnikanth (Indian Chuck Noris) converse to a shade of black:
0a00 00a0 0000 => #0a0000
On a lighter note
Chuck Norris doesn’t conform to web standards. Web standards conform to him. #BADA55
The WHATWG HTML specification has the exact algorithm for parsing a legacy color value.
The code Netscape Classic used for parsing color strings is open source: netscape/lib/layout/layimage.c.
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.
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 were added (in Netscape 4):
if (bytes_per_val > 4)
{
bytes_per_val = 4;
}
legacy-extract-an-encoding"
Commented
Nov 30, 2022 at 22:23
c is the only valid hex character in chucknorris, the value turns into: c00c00000000(0 for all values that were invalid).Red = c00c, Green = 0000, Blue = 0000.c00000 which is a brick-reddish toned color.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:
<table>
<tr>
<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>
</tr>
</table>
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:
Some examples:
oooFoooFoooF
000F 000F 000F <- replace, pad and chunk
0F 0F 0F <- leading zeros truncated
0F 0F 0F <- truncated to 2 characters from right
oooFooFFoFFF
000F 00FF 0FFF <- replace, pad and chunk
00F 0FF FFF <- leading zeros truncated
00 0F FF <- truncated to 2 characters from right
ABCooooooABCooooooABCoooooo
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
AoCooooooAoCooooooAoCoooooo
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="https://ajax.googleapis.com/ajax/libs/jquery/1.12.4/jquery.min.js"></script>
<p><input id="input" placeholder="Enter color e.g. chucknorris"></p>
<table id="result">
<thead>
<tr>
<th>Left Color</th>
<th>Right Color</th>
</tr>
</thead>
<tbody>
<tr>
<td> </td>
<td> </td>
</tr>
<tr>
<td> </td>
<td> </td>
</tr>
</tbody>
</table>
whippersnappersis absolutely a valid color code.