Magical gene / fields and regions

Tidemark

The belly and lower barrel filled to an arched waterline, with the line picked out in a second colour and a row of dots riding along it. A third allele carries the same marking worked in greys instead of white - dark where the pale form is light, and the same number of steps.

What it can come out as

OutcomeCarrying
TidemarkTdm/Tdm · Tdm/Tdc · Tdm/n · Tdm/Tdk
Tidemark, blackTdk/Tdk · Tdk/Tdc · Tdk/n
Tidemark, colouredTdc/Tdc
Wild typeTdc/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 893 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 pairShows asHow often
Tdm/TdmTidemark0.004% — 1 in 25,000
Tdm/TdkTidemark0.0053% — 1 in 18,751
Tdm/TdcTidemark0.0053% — 1 in 18,751
Tdm/nTidemark0.076% — 1 in 1,316
Tdk/TdkTidemark, black0.0053% — 1 in 18,751
Tdk/TdcTidemark, black0.0053% — 1 in 18,751
Tdk/nTidemark, black0.0053% — 1 in 18,751
Tdc/TdcTidemark, coloured0.0053% — 1 in 18,751
n/nWild type99.888%

Its gene carrot

The file

common/src/main/resources/horsegenetics/genes/tidemark.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.

Keyhorsegenetics.tidemark
Phasemagical — it adds signed colour in phase 3, after the pigment has resolved
Priority258 — where it sits in the one (priority, key) paint order
AllelesTdm · Tdk · Tdc · n
Varies per horse9 values drawn once off the expressing allele copy, so a foal that inherits the copy inherits the look
Built fromSPOTS, TOWARD, WAVES

Why it is built this way

Imported from the magic-gene intake, 2026-09-08. One sine wave read three times - the fill below it, the line at it, and a band just above it broken into dots by a spot field. Because all three read the SAME wave, the dots follow the waterline exactly however the arch knob is drawn, which three independent masks could not promise.

The black allele is the white one with the light taken out of it, and it sits one rung under white in the dominance series - so every combination that existed before it keeps the outcome it had, and only the pairs carrying Tdk are new. The re-toning is a mapping rather than a repaint: every achromatic target moves into the dark end of the scale keeping its order and its spacing, and every SATURATED one is left alone, because that colour is the gene rather than its lightness.

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.

Tidemark

One sine wave, three times over: the fill below it, the line at it, and a band just above it with a spot field multiplied in to break the band into dots. Because all three read the same wave, the dots follow the line exactly however the arch is drawn - which is the point, and is not something three separate masks could promise.

  1. the belly filled to an arched waterline — WAVES, painted with TOWARD
  2. the waterline itself, drawn as a line — WAVES, painted with TOWARD
  3. a row of dots riding along it — WAVES × SPOTS, painted with TOWARD

Tidemark, black

The same marking as the white form with the light taken out of it: a single near-black tone, and the coloured accents unchanged.

  1. the belly filled to an arched waterline — WAVES, painted with TOWARD
  2. the waterline itself, drawn as a line — WAVES, painted with TOWARD
  3. a row of dots riding along it — WAVES × SPOTS, painted with TOWARD

Tidemark, coloured

The same waterline with the fill and the accent in two colours the line carries. Fully recessive.

  1. the belly filled to an arched waterline — WAVES, painted with TOWARD
  2. the waterline itself, drawn as a line — WAVES, painted with TOWARD
  3. a row of dots riding along it — WAVES × SPOTS, painted with TOWARD

Wild type

No tidemark.

Paints nothing.