Adjust grey tone in error pages.

services/web/public/stylesheets/app/error-pages.less

@@ -65,7 +65,7 @@
 		.error-description {
 			font-family: @font-family-serif;
 			font-size: @font-size-h3;
-			color: @gray-light;
+			color: @gray;
 			margin-bottom: @line-height-computed * 2;
 		}
 		.error-btn {