Optimises the hex color validation.

Relates to clean-css#986

lib/optimizer/validator.js

@@ -15,11 +15,7 @@ var timingFunctionRegex = /^(cubic\-bezier|steps)\([^\)]+\)$/;
 var validTimeUnits = ['ms', 's'];
 var urlRegex = /^url\([\s\S]+\)$/i;
 var variableRegex = new RegExp('^' + variableRegexStr + '$', 'i');
-
-var eightValueColorRegex = /^#[0-9a-f]{8}$/i;
-var fourValueColorRegex = /^#[0-9a-f]{4}$/i;
-var sixValueColorRegex = /^#[0-9a-f]{6}$/i;
-var threeValueColorRegex = /^#[0-9a-f]{3}$/i;
+var hexColorRegex = /^#(?:(?:[0-9a-fA-F]{2}){2,4}|(?:[0-9a-fA-F]){3})$/; // https://regexr.com/3tdfg
 
 var DECIMAL_DOT = '.';
 var MINUS_SIGN = '-';
@@ -368,7 +364,7 @@ function isFunction(value) {
 }
 
 function isHexColor(value) {
-  return threeValueColorRegex.test(value) || fourValueColorRegex.test(value) || sixValueColorRegex.test(value) || eightValueColorRegex.test(value);
+  return hexColorRegex.test(value);
 }
 
 function isHslColor(value) {