There are various theories on why species living in darkness may have pigments that are capable of reflecting colored light, some of which we have already heard. Perhaps these life forms evolved in shallower seas, where light and color existed, and the pigments served a useful function back then. The transition to abyssal habitats may have occurred later, in which case the pigments are simply vestigial remnants with no current purpose, like the human appendix. The problem with that theory is that the colors and patterns of modern shallow water organisms should still be serving the useful function for which they originally evolved. That seems questionable. It is interesting though that most species of animal life found in subterranean caves are without pigmentation. There are pure white fish, crustaceans, insects, molluscs, and various other forms. Why hasn't the same sort of thing happened in the dark abyssal ocean? Beats me. Another theory is that shell colors are simply accumulations of certain metabolic wastes. In other words, color is not the purpose of the pigments, just a by-product. The problem with this idea is that many species show a broad range of color and markings even within one population. Do the lighter colored specimens produce less metabolic waste than the darker ones? Do albino specimens produce no waste materials at all? Akin to that theory is the idea that the colored substances do serve a useful purpose, but a purpose unrelated to their color, and the color is, again, simply a by-product. This has been mentioned recently, relative to the possibility that some pigmented substances may strethen certain parts of the shell. This is like the question "why is blood red?". If you approach this question with the idea that redness itself is an evolutionary advantage, you may come up with some interesting theories, but you won't find the answer. Because blood did not evolve "redness" - it developed oxygen-transporting capacity. It just so happens that oxygenated hemoglobin reflects red light, but that fact is entirely incidental to the animal's welfare, or to the purpose of hemoglobin. The same may be true of shell and other animal pigments. They may serve various functions, and their light-reflecting properties (that is, their color) may be entirely incidental and without any specific purpose at all. In the same vein, we might ask why so many species have brown opercula. Is brown more advantageous than other colors? Does it serve to camouflage the foot? Does it blend with the color of the sediment? Of course not! Toughness is the requirement for an operculum. Conchiolin is a tough, semi-rigid, wear-resistant material, and snails have developed the ability to produce that substance. It happens to be a brown substance. Period. Sometimes we just look too hard, or take too much for granted before we start looking. Paul M.