I pretty much use gray thread in 8/0 Uni for every fly. Grey blends in with everything. If it doesn't blend, it makes good segmentation. The only difference is if I want a differnet colored head for the fly.

I have made para-adams (2 dozen) with bright pink thread (was making Sierra Bright Dot flies just before). they caught just as many fish as any other adams. (I like the pink heads too)

As others have said...too much hype.