The term flaxen may refer to two separate definitions. The first and most often used, is a reference to a specific modifier which genetic cause is still unknown. It only works on chestnut based horses, and is responsible for lighting the mane and tail while leaving the coat colour largely unaffected. The result is a chestnut horse with flaxen mane and tail, which may range from a striking pure white to yellow or orange. While the coat remains within the normal chestnut range, it is possible the flaxen may more or less lighten the lower legs and belly of the horse, much like pangaré does. This variant of flaxen appears only on chestnut based horses, and leaves the black and bay based colours unaffected.
The second, less often applied variant also uses the term flaxen as a means to describe a lighter mane or tail, though in this context it is not limited to a chestnut base colour and may expand to bay and black. While the overall effect may be similar in appearance, the colour change is likely the result of a different gene. The most common causes are often silver or some variant of sabino, though other genes may be at work too.
In this article, we describe flaxen in the first context, referring to the chestnut based modifier.
Flaxen is often abbreviated as F or f, though its genetics remain largely unknown. It appears to be recessive, possibly polygenic (meaning more genes or alleles could be at play), which would explain the wide range of colours possible. Whatever the cause, the gene is widespread among horses, appearing in almost every breed. In some cases, it is seen as a basic requisite of the breed, as with the haflinger horse, which are all chestnut flaxen. Due to its recessive nature, combined with the similar principle behind chestnut, it is both very easily bred for, and very hard to remove from a population.As flaxen has a wide colour reach, its effect can both be very minimalistic and extreme in contrast, ranging from a colour very similar to that of the coat, to nearly snow white. The most striking appearance is easily the liver flaxen chestnut, where the body can be a very dark chocolate brown to black, and the mane and tail may lighten to a dirty broken white. This effect, caused by a combination of flaxen, chestnut and an unknown gene often denoted as 'sooty', is the most common colour in the black forest horse, and also quite popular in breeds like the morgan and the arabian horse. Unsurprisingly, flaxen chestnuts, and liver flaxen chestnuts in particular, are easily mistaken for silver dapples.
As flaxen is recessive, it is denoted using the lower case letter 'f'. The absence of flaxen in an allele is written with the capitalized 'F'. It is only visible on chestnut based horses, so the genetic code of chestnut flaxen horse would be 'ee ff'.