If Collingwood wear the mostly-white guernsey from last week with white shorts, then there is no clash.
I doubt it'll be a problem because we've got a mountain to climb just to make the GF. But if Collingwood pull off a miracle tonight, then I wouldn't have any objections to us wearing the predominantly white guernsey. Personally, I'm not too fussed about the predominantly white versus predominantly black debate. Provided they're black and white stripes, I'm happy. I reckon most Collingwood supporters are the same.