Javascript - "One shade darker"

Question

Is it possible to use javascript to determine what color is one shade darker than the current background? Maybe some hexadecimal addition/subtraction?

I have a menu that can be any color and if it wasn't too difficult it would be great if the submenu could be one shade darker. Does anyone know how to achieve this effect?

Answer 1

Something like this:

function shadeColor(color, shade) {
    var colorInt = parseInt(color.substring(1),16);

    var R = (colorInt & 0xFF0000) >> 16;
    var G = (colorInt & 0x00FF00) >> 8;
    var B = (colorInt & 0x0000FF) >> 0;

    R = R + Math.floor((shade/255)*R);
    G = G + Math.floor((shade/255)*G);
    B = B + Math.floor((shade/255)*B);

    var newColorInt = (R<<16) + (G<<8) + (B);
    var newColorStr = "#"+newColorInt.toString(16);

    return newColorStr;
}

Usage:

var newColor = shadeColor("#AA2222", -10);
alert(newColor); //Results in #a32020

Here is an example code to test it: http://pastebin.com/g6phySEv