You can try a new supplement called Vein Away. Its great. You can build all the muscle you want while shrinking your veins.
Kidding..... Agree 100% with atomini. It has to do with body fat. Some AAS will make you retain water and that will temporarily "hide" your veins but there isn't anything out there that I'm aware of that will not make you vascular. You need blood flow to build muscle
--Sprint