My own experience with pigments are that some cover better than others.
Black and white cover very well, and don't forget you can mix the two together to get various shades of grey.
Yellow is a tricky colour to avoid a streaky finish for some reason.
You can get small quantities of pigment at Alec Tiranti's. It does work out more expensive compared to buying larger quantities, but unless you are going to be producing hulls for sale, you won't be using much anyway.
Black and white are the two most useful pigments IMO, but if you want a bright colour then stick with the primaries e.g. red, yellow and blue, with those you can then mix any shade of pigment you want within reason.