it depends on the species. some species will have little to no variation in color beyond random mutation that may or may not be genetically passable. Some species do have natural color changes and you can indeed breed this down. You can strengthen a color or keep it consistant but its rare to make any "new" colors. these should all be ones naturally available. perhaps if you breed for 10 years you can see a change. this hobby is not quite old enough to know 100% but yeah, generally you can only get colors that are seen- you can just make them breed truer.
youd have to know their parents and the females color. and the general color of the brood, then youd have a general idea. males will definitely have color genes it just doesnt show up in their color. so you have to breed several lines to see what the resulting males are like. In my opinion you would want to breed X color female to males and then keep trying until you see a clutch that is mostly the color youre looking for, then select several males, and mate them to females from another breeder of the color the batch generally was, and then select the best of their clutch, and so on. it would be harder to get color info on males so if you do that part yourself, getting females elsewhere that youd want will be easier.
