I think it looks fine. I do a really bad job of matching colors myself, so you're doing better than I do. As for the sporran belt, I myself tend to wear a thin leather belt with ~6 inches of large link chain on both ends, it doesnt cut at the kilt like an all chain belt, and looks good with just about any sporran, formal or casual.

I've got 3 different belts i wear with my kilts, one is the standard 2.25 inch wide with the flat plate buckle, one is just a 1.5 inch wide leather belt like i'd wear with normal pants, I usualy wear this with my non-tartan kilts, and the last is a 3 inch wide ranger-style belt, which I cant decide if it looks more formal or less formal than the 'standard' kilt belt. I've just always liked ranger-belts.