Question, I have been fishing for over 40 years and this year a buddy of mine has gotten me so dead set on fly fishing now. It is something that I have wished I done years ago. Anyways, what makes a fly color "the one" for the day?

For instance, one day I could throw a Red Copper John and hammer the trout. Then it does nothing but if I change to a gold color or brown, that one works. What is that you guys do to say, hey today looks like a red day versus a copper or silver one. I know the old saying, dark days, dark colors but sometimes it not true. Appreciate any input. Be safe on the water! Right now I am at about 21" for my personal best bow in a river.