There's no performance increase/decrease that coincides with the color of fiberglass. One thing that can come into play is when clear fiberglass is used, and the veneer wood is something that just looks nice, but has poor performance properties. It that case the pretty wood just adds mass to the limbs, that can possibly slow it down, but that's the wood used that make the difference, not the glass. If you make 2 identical bows, and in both use the same limb laminations, but one has black or brown, and one has clear, they will both perform the same.