Like all things in life, there is no set formula as to when certain things should happen and when they shouldn't.
Just because you have a baby tiger that is smaller and has color, doesn't mean this one should have color by that size. It's all genetics. Give it time, I'm sure he'll color and be a red or tiger. Hell, he may even turn out to be a Wild Oscar (get ready for some serious aggression). A zebra Oscar, though? Sounds like an LFS is working some sort of scam, or it's a dyed fish. Which I hope isn't the case.