The answer begins:
“Certain shellfish, such as lobsters, turn red when cooked because they are red to begin with – we just can't see it.” (New Scientist, 7th Dec 2013: 69)Apparently the red colour is due to a compound called astaxanthin, which is there all along. Its effect is masked in live crustaceans by various other compounds. When the creature is boiled many of these denature, but astaxanthin is stable at high temperatures, so does not break down, and the lobster turns red – or its natural red colour is revealed.
Compare with Travis on brown leaves painted green: pp. 171 ff. of Travis, Charles. 1994. On constraints of generality. Proceedings of the Aristotelian Society 94:165–188.