Magical gene / ground and strong white

Koi

Hard-edged patches the way a koi carp is marked, with nothing blended at their boundaries and the mane and tail striped to match. The white variety covers the horse in two fields; the other two lay their patches on the coat and leave the rest of it showing.

What it can come out as

Outcome	Carrying
Koi	`Koi/Koi` · `Koi/Kob` · `Koi/Kow` · `Koi/n`
Koi, dark	`Kob/Kob`
Koi, white	`Kow/Kow`
Wild type	`Kob/Kow` · `Kob/n` · `Kow/n` · `n/n`

How each one is actually drawn - region by region, and the layers it is built from - is on the coding tab.

Crossing two of them

Finding one

About 1 in 3,571 wild horses is born showing this. That is the whole of the supply: catch one, or make one with the carrot below. Breeds set their own pools and a breed built around this gene will carry it far more often than the wild population does.

Wild pair	Shows as	How often
`Koi/Koi`	Koi	0.001% — 1 in 100,000
`Koi/Kob`	Koi	0.002% — 1 in 50,000
`Koi/Kow`	Koi	0.002% — 1 in 50,000
`Koi/n`	Koi	0.019% — 1 in 5,263
`Kob/Kob`	Koi, dark	0.002% — 1 in 50,000
`Kow/Kow`	Koi, white	0.002% — 1 in 50,000
`n/n`	Wild type	99.972%

Its gene carrot

The file

common/src/main/resources/horsegenetics/genes/koi.json — a data-driven gene, not a Java class. It is listed in the index.json beside it and registered by Genes' class initialiser at startup.

Key	`horsegenetics.koi`
Phase	magical — it adds signed colour in phase 3, after the pigment has resolved
Priority	218 — where it sits in the one `(priority, key)` paint order
Alleles	`Koi` · `Kob` · `Kow` · `n`
Varies per horse	5 values drawn once off the expressing allele copy, so a foal that inherits the copy inherits the look
Built from	PATCHES, STROKES, TOWARD

Why it is built this way

Imported from the magic-gene intake, 2026-09-08. One PATCHES field and its inverse, so every texel is one colour or the other. There is deliberately no third tone and no soft edge anywhere: a koi with a gradient in it is a paint horse.

Three alleles rather than two - orange dominant, dark and white each recessive homozygotes. The dark and white forms are not carriers of each other; a Kob beside a Kow is an ordinary horse, the same rule the LUT locus uses.

Only the WHITE variety covers the horse. The orange and dark varieties used to carry a second layer painting 'the dark patches, in what the bright ones left' - the complement of the first - so the two tiled the horse and no base coat showed anywhere. That layer is gone from both (owner's call), leaving the bright patches as actual patches against the horse's own colour. The white variety keeps it, because white-against-colour is the variety whose whole point is the hard boundary between two fields.

What it paints

Each outcome, described the way the gene file describes it, and then the layers that draw it in the order they are painted. The prose is the part a reader checks a bake against; the list underneath is what the engine actually did.

Koi

Orange against black, in patches a few units across with edges as hard as the vocabulary allows. The two layers use one patch field and its inverse, so every texel is one colour or the other and there is no third tone anywhere on the horse.

The bright half uses a hue knob capped at 60 degrees, so it runs red through gold and never reaches green. A koi that is not warm is not a koi.

the bright patches — PATCHES, painted with TOWARD
the mane and tail striped to match — STROKES, painted with TOWARD

Koi, dark

The same patchwork with the bright half taken down to a deep colour instead of orange - a koi read at dusk. Recessive to the orange form; two copies.

the bright patches — PATCHES, painted with TOWARD
the mane and tail striped to match — STROKES, painted with TOWARD

Koi, white

White against the colour instead of orange against black - the pale variety, and the one that shows the patch edges most clearly. Recessive; two copies.

the bright patches — PATCHES, painted with TOWARD
the dark patches, in what the bright ones left — PATCHES inverted, painted with TOWARD
the mane and tail striped to match — STROKES, painted with TOWARD

Wild type

No patchwork.

Paints nothing.