Ask around at any sheepdog trial and you will hear it. The red dogs run hot. The merles are clever but quirky. Blue-eyed dogs lose stock at distance. Coat colour is the most visible thing about a Border Collie, so it attracts explanations the way a fence attracts briars. The honest answer from behavioural genetics is simpler and less romantic: there is no evidence that coat colour changes how a Border Collie herds. What produces working style is a polygenic behavioural architecture shaped by selection on work. What produces colour is a small set of pigment loci inherited on its own terms. The two systems barely speak to each other.

That answer matters practically. Buyers pass over sound puppies and pay premiums for others on the strength of a shade. Breeders cull or keep dogs for reasons that have nothing to do with how they will read a ewe. And owners misread real problems, especially the genuine health issues attached to certain patterns, as temperament. It is worth separating what colour tells you from what it does not.

Is There Evidence That Coat Colour Changes Herding Behaviour?

No. Not in the sense the folklore means. There is no controlled study, and no plausible mechanism, linking a red or merle coat to the components that define herding style: eye strength, outrun shape, biddability, grip, or distance work.

The contrast in genetic architecture is the whole point. Herding behaviour is a polygenic trait. Our own estimates put the heritability of eye intensity in the moderate range, spread across multiple loci of small effect, which is why two littermates can work so differently and why selection has to act across generations rather than single matings. We cover the genetic roots of the Border Collie eye in detail elsewhere, but the short version is that the trait behaves like height in humans: many genes, much recombination, no single switch.

Colour is the opposite kind of genetics. A handful of well-characterised loci in the pigment pathways determine whether a dog is black, brown, red, diluted, merled or ticked. These variants segregate essentially independently of the loci underlying behaviour. A puppy does not inherit “red and hot-headed.” It inherits a recessive-red allele at one locus and, separately, a recombined sample of its parents’ behavioural variants. The coat is a caption on the photograph, not a summary of the plot.

Where Does the Belief About Colour and Working Style Come From?

The folklore is not stupid. It grows out of real correlations that people read backwards.

Colour tracks line, and line tracks style. Coat colour is not randomly distributed across the Border Collie population. Merle is common in sport and show kennels, where appearance is selected alongside athleticism. Certain farm families fix a colour simply because a closed breeding line carries it. So when a handler meets three brilliant merles from sport lines and three plain black dogs from hill farms, the obvious difference is colour. The operative difference is what each line was selected for, which the eye cannot see at a glance.

Colour is visible; behaviour is not. Humans are wired to attach causes to what they can observe. A dog’s coat is available to every bystander; its pedigree, early exposure and training history are not. When an explanation is needed, the visible trait absorbs it.

Confirmation finishes the job. Once “reds are hot” is in circulation, every fast red dog confirms it and every steady one is forgotten. Handlers are scientists in the field, but field impressions without records are the raw material of myth.

The One Real Adjacency: Pigment and Sensory Health

There is exactly one place where colour genuinely touches work, and it is a health matter, not a style matter. Dogs bred merle to merle produce homozygous “double merle” offspring at predictable rates, and those dogs carry elevated risk of congenital deafness and ocular defects. The figures are documented rather than anecdotal: in a sample of merle dogs across breeds, double merles showed about 10% unilateral and 15% bilateral deafness, versus 2.7% and 0.9% in single merles, a pattern catalogued in the Online Mendelian Inheritance in Animals entry for merle.

A deaf dog or a visually impaired dog will absolutely work differently: it misses whistles, loses stock at the edge of its field, hesitates on long outruns. But that is a change in sensory input, not in herding style. The instinct, the eye, the biddability are untouched. A sound red dog and a sound black dog with the same pedigree and the same start on stock are, for practical purposes, the same proposition. The lesson cuts both ways: never buy a double-merle puppy sight unseen for a working home, and never reject a healthy single merle because someone once heard merles are flighty.

Sensory problems also get misread as other things. A hearing deficit in a young merle can look like stubbornness; fading vision in an older dog can look like lost nerve. If a working dog’s behaviour changes, rule out the eyes and ears before you reinterpret the dog, and remember that motion vision and distance perception are working equipment, not personality.

What Does a Coat Colour Label Actually Describe?

Strip the folklore away and a colour label is doing one precise job: naming a pattern of pigment distribution. Under the labels sit two pigments, eumelanin (black and its derivatives) and phaeomelanin (red and tan), a set of genes that place, dilute or mask them, and patterning systems like merle, brindle, white spotting and ticking that decide where on the body each pigment is allowed to appear. “Red” can mean a recessive-red dog that cannot produce black hair at all, or a liver dog whose pigment is brown throughout; the word alone does not tell you which, and it certainly does not tell you anything about the dog’s character.

That separation, description on one side, inference on the other, is the correct discipline for reading any Border Collie. For owners and breeders who want the descriptive half done properly, a reference built on what coat colour describes walks through each colour and pattern of the breed as what it is: a coat, documented without drawing conclusions about temperament. Use the label to name the dog. Use the pedigree, the parents’ records and the dog on stock to judge it. The coat is real; the story attached to it is optional.