Retaining some of their black pigmentation while losing most of it.(adjective)
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Use "hypomelanistic" in a sentence
"The price for a hypomelanistic boa constrictor, one with a mutation that lightens its skin tone, was $99 on Feb. 1, down from $5,000 in 2007, on Kingsnake. com, a classified-ad site that acts as a market-maker for snakes."