Revert "Fix the Plus button default color"

This reverts commit 2d64b75777b35428a2a4da757fe563daea0f6283.

css/tarteaucitron.css

@@ -643,7 +643,7 @@ span#tarteaucitronDisclaimerAlert {
 #tarteaucitronRoot .tarteaucitronPlus::before {
     content: '\271b';
     display: inline-block;
-    color: #333;
+    color: white;
 }