I can't decide if my starter grew a krausen or if its infected. Its White Labs 566 - Belgian Saison II. I've never had a starter grow a krausen layer let alone a krausen layer with blackish-brownish spots.
Did you use a stir-plate to agitate it? If you did not, I am not surprised that your 566 grew a krausen. I just pitched this yeast yesterday and it is crazy aggressive!
As long as it smells good, pitch it. Be sure to use a blow-off tube with this one as well. I am glad that I did for mine.
I don't use a stir plate. I made a starter with this yeast once before and it didn't krausen up. But that one also had Orval dregs in it.
I got paranoid about the blackish spots and I had to hit the homebrew store for more rice hulls anyway. So I bought and pitched a new vial. I'd rather spend the extra money and under pitch than risk it being moldy.