Regarding the ordinary mepps and the long version I have not seen any difference when using the silver, gold or copper blades. Some say you should use the silver in coloured water, copper in clear water etc. I have tried it all, but in my experience I do not think that it makes any difference. This is my opinion after using them for years on the small spate river that I fish mainly for seatrout but catch salmon as well.
If the majority have been using bright colours before you try a more somber colour such as black in a small size.Have noticed that in lower water fish will only react and follow the really smallest of lure