Jaguar color change

[Aste88]

As far as I know carpets actually get brighter with age.

It's true that the jag gene comes from coastal so it's a cross between Morelia s. variegata (darker color) and Mcdowelli, as said the bright yellow are generally M. s. Chenyei (jungle carpet). Bottom line, best guess you have to know how it will turn out is looking at the parents' pictures.