Ever since water temps have started to drop and things are moving slower, I have noticed a need for changing colors as the day goes on.  For instance, the other day, we were catching them pretty much consistently on green salamanders (not a bait I often use in the fall), but as the day went on, the bite slowed until we switched to black/blue.  I have noticed the same pattern on crank baits.  Is this just a strange situation I happened to notice or does this have any truth to it?  It was a cloudy day, occasional sun, but for very short periods.  It was calm early on, but a 10 mph wind did pick up. 

It is very common for the most productive color to change though out the day.

I think color is related more to ambient light than any other factor and with this being fall, the sun is shining on the water ater a different angle, affecting light penetration.

Now with what pegs said > light angle , light intensity and minerals and other things in the water all effect ambient light . Fish also learn to associate colors with danger over time .