Merle is a coat dilution that leaves behind patches of base color, while the rest of the coat is diluted to a lighter, faded, slightly textured shade. It may contain lots of holes and speckling. It can create isolated spots of dilution, especially on coats with minimal coverage, but it should have an overall holey, patchy appearance. Up to 90% of the coat can be diluted, and as little as 15%.
Everything covered by merle will be diluted, including markings. Markings may faintly show on the diluted areas, but aren't required to, similar to how markings may appear on albino coats.
Merle is a hard edged marking, but may have some feathering or fur texture, and it may have a slight halo.
The geno code for Merle is written as:
nMr or MrMr
Merle may express in up to two layers of dilution. There will always be the main opaque layer, but there may also be a secondary layer extending from the main layer that shows more of the original base color and markings. It can be thought of as a large, irregular, halo that can contain holes.