The crab spider Thomisus onustus. Some individuals are a most unspiderly color: they are hot pink. This allows them to hide in hot pink flowers — and ambush unwary bees. Other individuals are yellow, and hide in yellow flowers. Even more surprising, their colors are not fixed: move a pink spider to a yellow flower, and she can change her color to match.

– Olivia Judson
March 25, 2008
Evolving the Wow! Factor
NY TIMES
This article and her blog are really interesting and well worth reading.