I find with yellow since it is just a "mutated" gene of red you would end up with a good number of red - green is usually a blue/yellow, which again leads you back to green

I find if you use a multi, you could be able to aim to a larger variety of color though red and blue will remain the most dominant especially if the background is unknown. If you wanted to breed to show, multi I hear isn't the best choice... But if for another reason, find something that you could play around with (safely and still with the fish's health in mind of course) although words and reading are great educational means, hands on does help a lot.