I notice that a lot of times when my hens legs get dull, it’s when they are laying heavy. The hen pulls a lot of nutrition from her body to lay.  I think it has a lot to do with how healthy they are.

The bleaching of the yellow in hens absolutely has to do with time in production, take a look at these photos (link: https://afs.ca.uky.edu/files/evaluating_egg_laying_hens.pdf) from the University of KY

As far as bleaching in cocks I think it has a lot to do with sun bleaching and as scales age and raise away from the shank they appear lighter in color.