Whether or not it actually exists or could exist. Color combinations aside, etc.
I have 2...
I want a Giant Tiger Koi DoubleRay Crowntail... I want him to be HUGE, big ol giant size. Yellow and black koi pattern with cellophane fins speckled with black... Maybe even spattered with some awesome dragon scales. His pattern should be stable, and his rays should be long and beautiful. He should have a very aggressive but protective personality, like a real tiger. He should love patrolling his tank and blowing bubble nests.
And then I wand a Halfmoon Doubletail colored like a Siamese cat... I want a nice long lean body, not the stubby body that a lot of them can get. I'd like nice full fins without a predisposition to fin biting. I want a nice cream colored body, with clean coloring. No marbling, no visible outline of the scales... and his fins will slowly melt into a milk chocolate color, and then rim the fins with just a thin black lace coloring. There should be NO iridescence to him at all. He should be milky and smooth and creamy, like pouring creamer into coffee.