Percent Diff between two colors for RGB.

colordiff.js

String.prototype.format = String.prototype.format || function(){
    var format = this;
    for (var i = 0; i < arguments.length; i++) {
        var arg = arguments[i];
        if (arg === null || arg === undefined) arg = "";
        var regex = new RegExp("\\{" + i + "\\}", "g");
        format = format.replace(regex, arg);
    }
    return format;
};

(function( exports ){
        "use strict";

	function colorHex( num1, num2, color ){
		return parseInt(( color || "" ).substr( num1, num2 ), 16 ); 	
	}

	var colorRed = colorHex.bind( this, 0, 2 );
	var colorGreen = colorHex.bind( this, 2, 2 );
	var colorBlue = colorHex.bind( this, 4, 2 );

	var ColorDiff = (function(){

		function ColorDiff( colorA, colorB ){this.colorA = colorA; this.colorB = colorB;}
		
		ColorDiff.prototype.toString = function(){
			return "{0}, $red: {1}%, $green: {2}%, $blue: {3}%".format(
				this.colorA, 
				this._channelDifference( colorRed( this.colorA ), colorRed( this.colorB )),
				this._channelDifference( colorGreen( this.colorA ), colorGreen( this.colorB )),
				this._channelDifference( colorBlue( this.colorA ), colorBlue( this.colorB )));
		};
		ColorDiff.prototype.copySCSSInstruction = function(){
			var instruction = "scale_color({0})".format(this.toString());
			copy(instruction);
			console.log(instruction);
		};
		ColorDiff.prototype._channelDifference = function ( colorA, colorB ){
			var basis, diff, percent_diff = 0;

			if(colorA > colorB){
				basis = colorA;
		    	diff = colorA - colorB;
			    percent_diff = -( diff / ( basis / 100 ));
			}

			if(colorA < colorB){
				basis = 255 - colorA;
			    diff = colorB - colorA;
			    percent_diff =  diff / ( basis / 100 );
			}

			return percent_diff.toFixed(2);
		};

		return ColorDiff;
	}());

	exports.ColorDiff = ColorDiff;
}(this));

colordiff_sample.js

var diff = new ColorDiff("95B8E7", "E6F1FD");

diff.toString()