I agree with SO many factors involved. I think the breeder holding it those first 8 wks (a little more as it gets a little older) are the most important.
But then, they can change from household to household. Hectic to quiet or vise versa. Their personalities are formed by their parents but development is started by breeder (tamed or not). But even that can be changed by amount of care & time spent with them or not spent with them, by new parent/s.
BUT, as with all living things, everything changes with time. Gliders do also. Earlier in breeding, Some gliders that I have thought will never trust me, took 2 yrs then boom, all of a sudden!
As breeding can affect them quickly,(new girl in town & boys act like goofs). (but nothing new there
A new joey, a new neighbor, changing cage/location/environment, change of enrichment both/either diet and exercise, to mention a few, can all change the life and form the personalities of our babies.
Then again, could be, that because of difference/higher cost, leu babies could just be held more from birth.
My lues are from extra sweet lines and that does matter! But does not 'always' come into play.(must admit-..Rarely
So yes, I believe good 'lines' are a big factor. Breeders involvement, and amount of unconditional love by new parents, all a must. But colors-No.