Question about the day and date wheel on a DD

[Fujiman]

While I'm not likely to ever buy a used DD (never say never, right?), The only dials that interest me are the silver stick or white stick. However, I've noticed on many used DDs that the background color on these wheels seems to be really dark while on others it's nice and bright.

Not being remotely an expert on the internals of the DD, I wonder what's the reason for it. Hopefully, I'm clear on what I'm asking. I tried to grab some example images from chrono24 and bob's watches but those sites don't seem to allow it. Instead of view picture, they're just links.