In my experience, Grapevine historically has not been a lake that fishes exceptionally deep (25+'), so I would suggest that if the surface temp is above 50, I would fish all the brush I could find from 10 - 25'. As for the very dirty water; the fish have to eat regardless of water clairty, and you really have no idea how deep the mud goes in a given area of the lake (and yes, it will all end up on the bottom at some point), so fish the darker colors you have, fish them ultra slow (dead stik), and make them stink, because while crappie are a sight feeding fish, if that sensory is taken away, they will go next to smell. If they can't find your bait, you might as well be home "honey-doin". Hope this helps and good luck.
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Guy