Border Collie
Merle Border Collie: colors, genetics and the risks of double merle
By Casa Trufa ·
For information only: it does not replace a visit to your veterinarian.
Merle is a color pattern: dark patches on a diluted background, often with blue eyes. A Border Collie with one copy of the merle gene is healthy. The risk comes from breeding two merles: some puppies inherit two copies — “double merle” — and have a high chance of being born deaf, with eye defects, or both.
What exactly is the merle color?
It is the effect of a gene that dilutes pigment unevenly. Where it acts, the hair comes out lighter; where it doesn’t, the hair keeps its color. The result is that marbled coat, with dark patches on a gray or cream background, never the same in two dogs.
The same gene can lighten part of the iris: hence the blue eyes, or one eye of each color (heterochromia), or a single eye with two colors. It is striking, and in a single merle it does not affect eyesight.
What is the difference between blue merle, red merle and tricolor?
| Name | What it is | What it looks like |
|---|---|---|
| Blue merle (azul mirlo in Spanish) | Merle on a black base | Bluish-gray background with black patches |
| Red merle | Merle on a brown (chocolate) base | Reddish-cream background with brown patches |
| Tricolor | Black or brown, with white and tan | Three distinct colors, no marbling |
| Bicolor | Black and white, the classic | No tan and no merle |
| Tricolor merle | Merle with white and tan | Marbled, with tan markings on the face and legs |
The FCI standard — the FCI is the Fédération Cynologique Internationale — allows a variety of colors in the Border Collie, on one condition: white should never predominate. That is not an aesthetic whim, and it has to do with what comes next.
Why is breeding two merles dangerous?
Every dog has two copies of each gene, one from each parent. A normal merle has one merle copy and one that is not. If two merles are bred together, on average one puppy in four receives the merle copy from both: that is a double merle.
| Pairing | Expected puppies | Risk |
|---|---|---|
| Non-merle × non-merle | No merles | None from this gene |
| Merle × non-merle | Half merle, half not | None from this gene |
| Merle × merle | A quarter double merle | High: deafness and eye defects |
In a double merle the dilution is so strong that it leaves areas with no pigment at all. And pigment is not only color: the cells that make it take part in the development of the inner ear and the eye. That is why double merle dogs are usually very white and have a high chance of deafness, of small or malformed eyes, and of blindness.
This is not a theoretical risk, and care does not fix it: it is avoided by not making that pairing.
How can you tell whether a puppy comes from a safe pairing?
- Ask what color both parents are and ask to see them. If both are merle, walk away.
- Watch out for “cryptic merle”: some dogs carry the gene without it showing in the coat. A genetic color test settles it, and a serious breeder has one.
- Be wary of an almost all-white puppy in a litter of merles.
- Ask about hearing: the BAER test checks each ear separately.
Before you settle on a merle puppy, ask to see both parents and their genetic color test: that is how a double merle is ruled out.
Does a single merle have any health problems?
Not from being merle. A Border Collie with a single copy of the gene hears and sees like any other. Blue eyes don’t mean poor vision either.
What it does need, like any Border Collie, is the breed’s health tests in its parents: hip and elbow X-rays — the ACCC (Asociación Club Canino Colombiano, Colombia’s FCI member kennel club) requires a dysplasia diagnosis from 18 months of age — and the genetic tests for CEA (Collie eye anomaly), TNS and MDR1. Those tests say far more about a puppy’s future health than its color does.
Is a merle Border Collie worth more?
It is advertised at a higher price because more people look for it. In October 2026, one of the sites we consulted listed a merle at COP 2,800,000, at the upper end of the range for unregistered puppies. We record it, with sources, in the Border Collie price guide.
But color does not make a dog better, and a breeder who charges for heterochromia is charging for the photo. Choose on temperament and health; color comes after. And before any of that, check that this breed fits your life: can a Border Collie live in an apartment?
Frequently asked questions
Does the merle color cause health problems?
A single copy of the merle gene does not. The problem is double merle, which comes from breeding two merle dogs together: those puppies have a high chance of deafness and eye defects.
What is a blue merle Border Collie?
A Border Collie with the merle pattern on a black base: a bluish-gray background with black patches, often with blue or two-colored eyes. In Spanish it is also called “azul mirlo.”
Can Border Collies with blue eyes see well?
Yes. In a single merle, a blue eye or heterochromia is simply a lack of pigment in the iris and does not affect vision. The eye defects of double merles are a different matter.
Can you breed two merle Border Collies?
It should not be done. On average, a quarter of the puppies will be double merle, with a high risk of deafness and blindness. The responsible rule is to breed a merle only with a dog that is not merle.
Sources
Keep reading
From the guide to the breed