This was one of those projects where I didn't have my heart fully in to it. I must have started it about 10 years ago. It should be further along than it is, but at least it's back for now.
It started with the desire to get a very dark fish with some orange on it. Streaked Blacks were a fish that I thought would work for this. The streaked gene causes lighter areas to appear on black angelfish. The older they get, the greater the lighter areas grow. I guessed that crossing with a koi would give me a black that had orange showing through. I've known for quite some time that the skin layer that stores carotenoid pigments is beneath the layers containing melanins.
It did work, even from the beginning, but it didn't "wow" me. I'd get a speck of orange here and there, but usually just on the top of the head, if streaked happened to leave a light patch in that area. I set the project aside for more interesting things, so I ended up not making the number of selective breedings necessary to fix the trait. I needed to not only increase the orange expression, but I had to select for a more streaked effect.
I few years ago, I gave the stock to Dave (Hlasnick). He made a couple nice crosses and when he closed his fishroom he gave it back to me in better shape than what he started with. I've had it back for about a year now, and really like my latest cross. It's been a step up in the amount of orange.
The best cross appears to be a black splash to a koi for every breeding. If you double up the dark genes, there is less chance of light areas for the orange to show through. You could use a sunset, but the orange from a koi is brighter is my experience. I keep one black splash line, that changes each time I cross to a different koi line. Keep switching koi lines, and you'll be able to keep them vigorous long term.
This is the pair that produced the juveniles in these photos: