I've only caught a few ratsnakes in deep East/Northeast Texas, but of those several have been relatively anerythristic. I don't think it is a case of a simple anerythristic gene in the area but rather a clinal tendency to lose the background color.

This one is from Freestone County, TX.

There is a photo of a wild caught albino from Tarrant County on this website - http://www.uta.edu/biology/herpetology/Texas rat snake.htm
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Chris Harrison
San Antonio, Texas