I agree with the dark=patina concept for the lume, as mine (ca. 1969) has rarely been off my wrist since purchased new. It's seen many, many hours in sunlight and lived most of its life in S. LA where it it very humid. Since the watch is sealed I doubt if humidity would be much of a factor, though.
OTOH bezel inserts are the opposite as evidenced by my example below. The original (left) was actually on the watch for only about 10 years, then lost for a few years and stored out of sunlight since that time. The replacement (ca. ~1980) on right has many more years on the watch (~34) and is obviously not as faded. The color is more faded in both than is depicted in the photos.
