I know diet effects an animal's stats, but is it possible to raise a creature's stats enough through diet that when bred it can turn the stat from a regular black stat to a really good green stat? 

Thank you.  :)

Green stats are from certain genes, or genetic power. It does not come from the stat's number.

You can see a list of genes here. 

When you know what stat you want to be green and know what gene gives it, you can start breeding for that and or genetic power.