I am a novice at fish keeping, but in the reptile hobby that sort of mutation might be called hyperxanthic, or xanthic, or even hypomelanistic...and/or hypoerythristic. It is almost impossible to say what is actually going on without some serious testing. It will be interesting to me to see if this plays out to be a simple recessive or some sort of more complex inheritance. It is possible only one of the parents carries the genetic mutation, if the heritability is co-dominant or incomplete dominant. There are other possibilities too. Really cool thread.
The IG fish looks like hypomelanism + hypoerythrism to me, for whatever the heck that’s worth. Subbed.
My official psychic foretelling (totally joking) is that it will turn out to be a single co-dominant mutation that causes hypoerythrism and hypomelanism.
You’re going to have to produce a few more Trimacs to find out!