I believe they do. From the photos I've seen, of normals anyway, theyappear to get a somewhat dirty wash of melanin as they grow older. It's my understanding that they're at their most colorful at around age 2 or 3 years of age. If you do a search on Hercules (Marcel Poots' corn) you can see what an old corn looks like- not to mention an exceptionally large one.
Cheers,
Jason