I only fish rivers for Pike, where their main diet are Bleak, Dace and Roach. Therefore most of my flies are white or grey with varying degrees of sparkle tied into them, as Tailing loop as said White with a red head is also a favourite but sometimes i wonder if it's a case of whatever fly was on at the time was going to get hit, although i'm sure the red wouldn't put fish off over a plain white/grey fly...
My standard pattern(at the moment) has a zonker tail with the rest tied of synthetics giving bulk, they're also mostly leaded, again it's needed in the flow on rivers, plus a little jiggy action is no bad thing
I also tie it short in the summer and add a popper head, awesome fishing on a low river early in the morning and late in the evening
I've never been one for tying shocking coloured flies like the oranges etc, but that's just me, they do work and who really knows what they look like to the Pike eh?

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