This method reduces color strings to a minified version, e.g. '#FF00FF' outputs '#F0F', 'rgb(255, 0, 255)' also outputs '#F0F'.

minifyColor.js

function minifyColor(stringColor) {
	var rgb, slicedString, hexString;

	if(stringColor.indexOf('rgb') !== -1) {
		slicedString = stringColor.slice(stringColor.indexOf('(') +1, stringColor.indexOf(')'));
		rgb = slicedString.split(',');
		var hex = rgb.map(componentToHex);
		hexString = '#'+hex[0]+hex[1]+hex[2];
	} else {
		hexString = stringColor;
	}

	return reduceHex(hexString);
}

function componentToHex(c) {
	if( typeof c === 'string') c = parseInt(c);
    		var hex = c.toString(16);
    	return hex.length == 1 ? "0" + hex : hex;
}

function reduceHex(hexString) {
	var isValid = true;
	var hexArray = hexString.slice(1).match(/.{1}./g);
	var result = '#';

	hexArray.forEach(function(segment) {
		if(segment.charAt(0) === segment.charAt(1))
			result += segment.charAt(0);
		else
			isValid = false;
	});

	return (isValid) ? result : hexString;
}