Hi i have tried several thing too restore the colours but so far not much first i tried spirits, nope hardly works then i removed some of the keys and tried stronger thinners like the one found in paint powerfull stuff,witch i will not sugest it worked in some ways but not good enugh so i tried something even more powerfull(stupidity took over)and ended upp with melted plastics. i would sugest remove one key get the finest sandpaper available and try to rubb it off were you cant notice. if it works its go time if not make sure you have runbbed on a place were it is not too visiable..
sorry i could not help you more..
adonay :-D