Magical gene / mane and tail

Frostfall

Mane, forelock and tail losing their colour from partway down, ending white - and reaching it at different depths strand by strand, so the front is feathered rather than level.

What it can come out as

Outcome	Carrying
Frostfall	`Fro/Fro` · `Fro/n` · `Fro/Frc`
Coloured Frostfall	`Frc/Frc`
Wild type	`Frc/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 595 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
`Fro/Fro`	Frostfall	0.006% — 1 in 16,667
`Fro/Frc`	Frostfall	0.024% — 1 in 4,167
`Fro/n`	Frostfall	0.114% — 1 in 877
`Frc/Frc`	Coloured Frostfall	0.024% — 1 in 4,167
`n/n`	Wild type	99.832%

Its gene carrot

The file

common/src/main/resources/horsegenetics/genes/frostfall.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.frostfall`
Phase	magical — it adds signed colour in phase 3, after the pigment has resolved
Priority	401 — where it sits in the one `(priority, key)` paint order
Alleles	`Fro` · `Frc` · `n`
Varies per horse	3 values drawn once off the expressing allele copy, so a foal that inherits the copy inherits the look
Built from	AXIS, PARTS, STROKES, TOWARD

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.

Frostfall

Value only - no hue anywhere in it. The roots keep the hair's own colour, the far ends are white or near it, and the middle passes through a neutral grey. The transition takes up something between a third and two-thirds of the length, so there is no line to point at; and because bundles of strands reach white at different depths, the front is interdigitated rather than a clean horizontal. The tail carries it furthest, the forelock least.

the value falling away down the hair — PARTS × AXIS, painted with TOWARD
the feathered front, strand group by strand group — PARTS × AXIS × STROKES, painted with TOWARD

Coloured Frostfall

The same marking in a colour the line carries rather than in white. Fully recessive: it takes two copies, and a single copy beside a white allele shows white. It never gives blue eyes, whatever the white form does.

the value falling away down the hair, in colour — PARTS × AXIS, painted with TOWARD
the feathered front, strand group by strand group, in colour — PARTS × AXIS × STROKES, painted with TOWARD

Wild type

No frost.

Paints nothing.