Lacing

Lacing appears as white webbing or reverse-dapples, usually along the back or topline but can appear anywhere on the body.

The lacing will always be lighter than the basecoat (or white), and can optionally affect mane and tail where it touches.

Non-heritable traits have a chance to occur on any foal and are rolled at random when the foal genotype is rolled.
As the name implies, non-heritable traits will not pass to offspring from the horse that has it.

Chestnut with lacing

chestnut