All of the solutions posted on this page are incorrect when the string in question is the same colour as the test colour. Granted, you could use a very unlikely choice of colour, but I would prefer to go for 100% success rate.
OP has a single typo in his code (see condition with colon), and does not test for "#28e32a", so that colour will fail, and the regex will collapse whitespace within the colour, so "#28e 32a" would (incorrectly) pass.
In normal JavaScript, this should have 100% success:
function validTextColour(stringToTest) {
//Alter the following conditions according to your need.
if (stringToTest === "") { return false; }
if (stringToTest === "inherit") { return false; }
if (stringToTest === "transparent") { return false; }
var image = document.createElement("img");
image.style.color = "rgb(0, 0, 0)";
image.style.color = stringToTest;
if (image.style.color !== "rgb(0, 0, 0)") { return true; }
image.style.color = "rgb(255, 255, 255)";
image.style.color = stringToTest;
return image.style.color !== "rgb(255, 255, 255)";
}
JSFiddle: http://jsfiddle.net/WK_of_Angmar/xgA5C/
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