I have always tied my spinner patterns for PMD's and BWO's with clear microfibets and they have worked well. On big stuff like drakes, I usually use a very dark set of tails.

I was watching Davie McPhail tie a very small spinner and he touted the use of black microfibets. I can see the logic of wanting them to stand out more while lying on the surface with the trout looking up.

Anyone have good evidence either way, other than assumptions?