While I don't catch many crappie around here, I have found color to be a small selection of what works and what doesn't. The main thing I have found is the brightness or the variation of the color can make more of a difference than anything. I finally decided to get a custom color combination for tying up my jigs and flies for salmon and steelhead. All 3 colors are proven catchers and the combination has proven to be the best I have ever used.
I believe that finding what works in your area and sticking with it will produce more fish than anything. The fish know what they like and for some reason hit whether it be it mimics natural food or they just can't resist it.
I do however firmly believe that slabs and lunkers will not fall for the same old thing a lot of the time. That is when that special jig that has sat in the box for a couple years has it's time in the water. Heavy fished water that have slot limits are classic examples.
Having a couple specialty patterns along with the old standby's covers most situations. I have a couple boxes full of 3 colors for jigs and flies for salmon along with 10 each of 3 "other" colors that when nothing else works they will.
Sorry I can't help more for crappie but I bet that crappie fishing works about the same way.
I love taking my kids fishing, now if I could just manage to fish at the same time.