To maintain basic colors is relatively easy. By basic I mean black lace, green, blue, cherry red, etc. Colors difficult to maintain are the ones that has NR genes in them like extended red, orange, yellow. The easier ones are white opaque and white platinum, and cambodian.
Say, for example you want to maintain extended red. DO NOT use anything with irid. It would be best to combine to a cambodian like color but without any irid (red-flesh body with solid red fins). You may even come up with orange ....
note: TBH I have never worked with red. This is based on what I see in friend's breeding.