Hi Patricia, Welcome!
As far as the colour changes, I have a three year old and he's still changing!?!? right now he's silver and gold, but he's developed black roots since his neuter a month ago!
I think theres a sticky here that has a ton of info on puppy colours and predicting outcomes.
There is also a sticky about food grades (A+, B, etc) I dont think science diet is that great. I currently feed my guy Orijen.
If you decide to change his food, do it gradually, adding more of the new a little at a time, this will help u avoid tummy upsets.
good luck!