I show and breed coloured horses, and it depends on the particular head of the horse. The purpose behind a fancy velvet browband is to help draw the judges attention towards your horse. However like i said it depends on the shape of the horses head and its breed.
I use a plain bridle from Fylde, I have a traditional cob. The bridle also has a flat hunter noseband which is more suited to him than a rolled stitched one. His previous in hand did have a brass clinch browband which also suited him.
All depends on the type of horse you have, but you can't really go wrong with a plain one. I have seen brass, plain and fancy velvets on horses in coloured classes.