My guess would be a melanistic coyote. One was killed down here in Texas a few years ago. Melanism is pretty well documented in many mammals (Black Jaguars AKA Black Panthers) although, you don't hear too many coyotes having it which would make it a very cool find. Another pigment issue is Leucism which is almost the opposite of melanism (complete opposite would be albino) I've seen several times in the wild. I shot these photos of a leucistic Red Tailed Hawk last year:
[Linked Image]
Full Size: http://farm6.static.flickr.com/5283/5247777744_cc08816530_o.jpg
and
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Full Size: http://farm5.staticflickr.com/4126/5396258581_f30cefd28a_b.jpg
If it is a Melanistic coyote, I'm betting the local F&G would be interested in the find; it's pretty dang cool.
JP