Board Thread:Support Requests - Designing Your Wikia/@comment-4224349-20150315181811/@comment-26209257-20150315181936

It's called CSS.

a[href="/wiki/User:A_Frozen_and_Smurf_fan"] {color:gold !important}

Add it like that, and make sure you have an underscore if the user's name has a space, so instead of using a space for the username, use an underscore.