There are many other variables to consider other than the glass color and possible light exposure. You'd have to do a test using the same cider in clear and dark bottles.
Is your keeved cider much sweeter than your dry cider?
Are they all aged on the lees and bottle conditionned? Do they have visually similar quantities of lees?
I
have also noticed that the body and taste of dry cider improves after
18 months-3 years in bottle, as in traditional method sparkling wine
(15 months for champagne and 3 years for vintage champagne). My theory
is a a lot of this is due to lees autolysis.