I've always heard the "silver for sunny" saying. It's always held true for me. That being said, if you're targeting coho or steelhead, there are just rivers that have "their color." Honestly, I pick my finish based on the water size, clarity, and colour rather than weather in most cases.
My rules:
Super clear rivers, small/clear water: copper fav, gold or brass otherwise
Clear large rivers: copper/colour (typically orange or pink), brass or gold with color (orange, pink, or chartreuse).
Rivers that have some sort of tint/color to them: straight silver or a silver/colour combo.
Lately when exploring, a great all around spoon is the matte or "white silver." In low and clear I'll leave them as is. In some rivers that have "a color" the fish like, or the water has lower vis, I have a few different colored sharpies in my pocket.
You really can't go wrong with silver/brass and silver/copper to cover pretty much anything you want though. Copper in clear, and brass to be seen are what I stick with.