The gene
Layers
Each layer is where (masks) times what (an effect). Masks multiply together by default, so add one to narrow the area and switch it to MAX to widen it.
Can a gene change the horse’s eyes?
No, and please do not try. A gene file has no mask, op or effect that reaches an eye, and that is deliberate rather than an omission. A horse’s eyes are thirteen ordinary heritable loci — iris colour, sclera colour, and the two halves of sectoral heterochromia, once per eye, plus the glows and the third eye. What colour a horse’s eyes are is something it inherits, not something a coat pattern decides.
The natural genes that used to paint an iris — cream, champagne, tiger eye, the four white loci — no longer do. They request an allele at the eye loci, and it is written onto the foal at birth, so a splashed white horse really carries the blue and really passes it on.
If your gene needs a particular eye, ship a breed with it — a breed can pin any locus, the eye loci included — or tell players which eye alleles to breed onto it. A handful of hand-written magical genes (dhampir, shadowcreature, light) do still paint eyes directly; they predate the loci, they are Java rather than gene files, and they are not a pattern to copy.
Effects
What a horse carrying this outcome does, as opposed to what it looks like. Effects hang off the outcome, so a two-copy horse and a carrier can grant completely different behaviour.
Export
Where does this file go?
Save it into .minecraft/phc/genes/ - the instance folder, for a launcher
other than vanilla's (for the dev workspace that is neoforge-26.1.2/run/phc/genes/)
- and restart. The folder is created on first launch and has a README in it.
Every file there is loaded in filename order, and each gene adds a segment to the genotype code — so adding or removing one invalidates horses saved before the change. That is expected while the mod has no save compatibility.
A file that fails to load is reported in the log and skipped; the rest still load.