Not just any colours but the ones of the German deck: Diamonds are orange because bells are orange, and spades are green because leaves are green. Also spades and leaves look almost identical anyway. Hearts are the same, and acorns become clubs.

And just to be pedantic: It's not the "tournament deck", it's specifically the tournament deck for Skat, adopted when the East and German leagues reunified to avoid confusion. You'll be hard-pressed to get your hands on a 6 or below in those colours because Skat uses 32 cards.

I do think it's a good idea in general, though.