ability to insert uppercase color names

lib/less/tree/color.js

@@ -151,6 +151,8 @@ tree.Color.prototype = {
 };
 
 tree.Color.fromKeyword = function(keyword) {
+    keyword = keyword.toLowerCase();
+
     if (tree.colors.hasOwnProperty(keyword)) {
         // detect named color
         return new(tree.Color)(tree.colors[keyword].slice(1));