Zotac is probably on par with Asus, Gigabyte and Gainward when it comes to quality and customer service. So that's halfway decent. Nothing like EVGA, but still pretty much ok.
Colorful is probably tending more towards brands like PNY, Galax, Palit, Inno3d, etc. Decent if the price is right but if the price is anywhere in the ballpark of a more premium brand, then not worth the purchase.