I've noticed this with my jungle too.. He gets a significant amount of extra peppering a few weeks before shed... and when he sheds it's gone and his yellows are extremely vibrant.
A lot of fun, you always get a lot more beautiful snake afterwards!
MH
Who the hell is Pat?
"Pattimuss doesn't run, he prances most delicately, like a beautiful but sad fairy, winged and capped, curly toed shoes on each foot, dancing on dewdrops while lazy crickets play soft music for him to keep time by...." - Wes