get-colors.js

var pseudoClassesAndElementsArray = ['', ':hover', ':focus', ':active', ':first-child', ':first-of-type', ':checked', ':disabled', ':empty', ':enabled', ':invalid', ':last-child', ':last-of-type', ':link', ':only-of-type', ':only-child', ':optional', ':out-of-range', ':read-only', ':read-write', ':required', ':root', ':target', ':valid', ':visited', '::after', '::before', '::first-letter', '::first-line', '::selection', '', ];
var colorListArray = [];

function isArray(data) {
	var isArrayBoolean = Object.prototype.toString.call(data) == '[object Array]';

	return isArrayBoolean;
}


function inArray(needle, haystack) {
	var length = haystack.length;
 
	for (var i = 0; i < length; i++) {
		if (haystack[i] == needle) {
			return true;
		}
	}
 
	return false;
}


function inStringRegex(stringData) {
	var regex = /rgba?\(.*?\)/g;
	var outputMatchedArray;

	if (!!stringData) {
		outputMatchedArray = stringData.match(regex);

		if (isArray(outputMatchedArray)) {
			outputMatchedArray.forEach(arrayElements);
		}
	}
}


function arrayElements(element, index, array) {
	if (!inArray(element, colorListArray)) {
		colorListArray.push(element);
	}
}


function callPseudoClassesAndElements(elementValue, index, array) {
	var domObject = document.querySelectorAll("*");
	//console.log(element);

	//runs through all dom elements
	[].forEach.call(domObject, function(element) {
		var propertyLength = window.getComputedStyle(element, elementValue).length;

		for (var i = 0; i < propertyLength; i++) {
			var propertyName = window.getComputedStyle(element, elementValue).item(i);
			var propertyValue = window.getComputedStyle(element, elementValue).getPropertyValue(propertyName);

			//console.log(propertyValue);
			if (typeof propertyValue != 'undefined' && !!propertyValue) {
				inStringRegex(propertyValue);
			}
		}
	});
}


//init
if (document.querySelectorAll && window.getComputedStyle) {
	pseudoClassesAndElementsArray.forEach(callPseudoClassesAndElements);

	console.log(colorListArray);
}
else {
	console.log("Es trat ein Fehler auf");
}