What colors work best in muddy water?

Contrast is what you're looking for in this situation.  Most fish
feed looking up.  If you're in stained water, a lure that
matches the color of the water would be your worst choice.  
On a cloudy day, with muddy water I like black & red skirts on
a spinnerbait that will throw off lots of vibration.  Big blades
along with darker color skirts usually will do the trick.

Don't forget that bass will hang tight to structure in muddy
water.  Cast dark colored jigs with trailers next to stumps,
logs, and bushes.  Bump your lure against the structure
when you can.  Also slow down your retrieve and
presentation.  Fish can track vibration and movement well in
muddy water.  Give them something to target on.