Make a Custom Dye? No

Apply a Dye to armor you made? Absolutely.

You can apply dyes to every crafted armor and dropped armor in the game. Even Clothing you steal can be dyed.

Just remember it is bound to you once you dye it. You can give it to an Alt Character, but you can't sell or trade it. Well you can sell it to an in game Vendor.

The only thing you can't dye are the costumes, weapons and shields.

Also, every dye looks different on each material and racial style, so try them even if you think you might not like them. And, you can change dyes as often as you want.