when i try to buy Sapphire primary gradient it says "This item cannot currently be brought" y?

This is cause sapphire primary gradient is a limited edition (there are only a few of them in the market, and will stay like this forever unless otherwise), and therefore cannot be bought. You could probably find a player to buy it from but it'd be costly. It's probably better to save up for textures rather than buying gradients as you'll eventually "need" them in the future if you would like to make yourself bling.