I am a geneticist; but I was hesitant to enter the discussion, having no direct experience with pink convict breeding. But conflicting observations reported here by Basslover34 and others on the web peaked my interest in the inheritance of pink in convict cichlids.
If the pink phenotype of convict cichlids was determined by a simple Mendelian inheritance model we could propose the following: Because the pink trait is determined by a leucistic mutation (more on this later) I will use L for the stripped (or wild type) pattern that is dominant. In the logic of this scheme, the pink color would be l. A convict with the pink phenotype has the genotype of ll. Note that the stripped gene L is not present and cannot be present if the inheritance model is true. Stripped convicts are either LL or Ll. But if L can not be present in ll pink convicts how can stripped individuals be found in the progeny? I believe that the paradox can be resolved by accepting the proposed model for inheritance, BUT rejecting the notion that the pink phenotype is a simple Mendelian trait.
The definitions of phenotype and genotype must be understood to see my point. The phenotype of a trait is what we see: eye color, a person's height, yield in corn, or wrinkled pea seeds to give a few examples. Of this list the Mendelian traits are eye color and pea seed texture. The expression of these two traits are each controlled by a single gene with dominant and recessive forms, so their genotype follows closely from the phenotype. In sharp contrast the traits of height and yield are determined by hundreds to thousands (10, 000 genes is the estimate for corn yield) of genes acting in concert. The genotype is unknown for these types of traits. Indeed, such genes are discussed in statistical and quantitative terms only.
So what of the pink convicts? Based on what I have read, I believe the pink convict phenotype is controlled by a few loci -- places on chromosomes where a specific gene is found -- of which one locus (gene) has a major effect on the trait. I would like to use the genetics of twinning in sheep as an example. Twin sheep is a trait contolled by three genes (loci). One gene has a major effect and explains some 95% of the variation in the trait. The other two genes each contribute about 2.5% of the variation. For decades, sheep breeders thought twinning was Mendelian because the one gene had such a large effect on the outcome of the matings. Only after a long and meticulous set of experiments were the other two genes identified.
Pink convicts are not albinos; they are leucistic. Albinos are unable to synthesize pigments while leucistic mutations make pigments but the deposition of the pigments is inhibited. The tell is eye color. Albinos have pink eyes, leucistic mutants have normal eye color. Look at the eyes of a pink convict and compare to the eyes of a white oscar. You will find the former is dark while the latter is red. Transportation, storage, and development of chromophores require countless enzymes, which are the realization of information encoded in the DNA as genes. It is not hard in this situation to imagine a single gene having a large effect on pigment deposition, but other genes that can partially circumvent the major gene's effect on phenotype. This model of inheritance, and the expression of leucistic muations helps explain, and is consistent with, the other pigment variant of convicts -- marble.
I am sad to say that I can not provide a better model. The number of minor genes and whether these various genes are dominant or recessive in their expression can only be determined experimentally. Pink phenotype strains that produce offspring with various expressions of dark stripping and marbling most likely are the second and later generations from parental combinations of (LL X ll) or (Ll X ll) or (Ll X Ll) parents and received the "other" genes influencing stripped patterns from the stripped parent.
From an innocent question, a bit of acrimony, and college genetics comes an interesting insight into pattern and color expression of a popular Central American cichlid. The genetics of pink convicts highlights the importance of the adage "Handsome is as handsome does" to the breeder of fish.
