I imagine it's a simple matter of visual contrast. Using your own example, if the cladding on a Kaiser has "grayed" a little, the amount of contrast between the charcoal gray paint color and the cladding color isn't going to look as pronounced as it would if it were on an Ebony. That would be the baseline to consider first in my opinion, with multiple variations in the products used for cladding care by previous owners accounting for most of the other differences you've seen.