I had ramirezi not bred. But I had to take pictures with breeders from our former club, if they wanted to make a presentation. I liked the fish always. But I had the water too small. It was the ancestral form, cacatuoides.
There are still among the offspring more yellow? And you have yellow couples recognized for breeding?
It may be a mutation. But that's very rare.
It must eventually had trunk with color variations connection with parents. Today there are all colors, blue, orange, red. The lemon yellow I have not yet seen.
If it is dominant, the yellow color is back. If recessive, so it is covered by the normal color. (The phenotype). But in the genotype the property exists, and may occur by chance again.
These genetics is complicated. And practice this takes a lot of time and patience