I have been told that smallies will change color to match the areas they have been in. A lighter color will be a fish that has been in/near sunlight/lighter areas, whereas the darker colored fish has been staying in a darker area (under ledges, logs, etc). Natures way of camo for the fish. For the most part, I've found this to be true.

Here is a fish from shallow water where the sun was hitting:


Another fish from the same area that was caught from a deeper pocket under a rock ledge:


Dinstinct difference in the coloration of the 2 fish.