The dun colours are the result of the dun diltion gene's unique effect on the basic coat colours. The four basic coat colours are black, brown, bay and chestnut. Traditionally, only three base colours are recognised; black, bay and chestnut.
The dun dilution gene dilutes the base colour to shades that may appear the same as certain cream dilute colours. But it is distinctively different in a number of ways from the effects of the cream dilution gene. The main difference is dun markings or factors. All dun horses must have at least a dorsal stripe and leg barring. The rest of the possible dun markings a dun horse may have can include concentric rings on the forehead (cobwebbing), masking on the face, transverse stripe or bar over the withers, neck cape or shadow, fishboning on the neck, dorsal barbs that are perpendicular to the dorsal stripe, light ear tips (on the back side of ears) and barring on the ears.
Another main difference is the lack of true gold colouring. The dun gene dilutes the base colours to shades of dove or mouse grey, light tan, yellow, or apricot. The dun colours have a yellow or tan/yellow tone, whereas the cream dilutes have either gold or gold/yellow tones.
The dun gene is not related to the cream gene at all. The cream dilution gives us smoky blacks, brown (or seal) buckskins, buckskins, palominos as well as the double cream dilute colours of smoky cream, perlino and cremello. You cannot produce a dun horse from horses that are one of the cream dilute colours. It is possible to have horses with both cream dilute and dun dilute genes (like Oty), if one parent was a dun and the other a palomino, the offspring will carry both genes. For example, a buckskin that also has a dun gene is most often called a dunskin, and a palomino with a dun gene is generally called a dunalino. A cremello or perlino with dun markings is also possible - see them, and others at the first link listed below.
With Otoe's breeding, I thought he had to be homozygous dun (two dun genes dominant), but he has produced 1 double dilute (white horse) when put to a Cremello a few years ago. However, I have put him over palominos and got 2 dunalinos; a perlino and produced a buckskin; and 2 buckskins producing a buckskin or dunskin & a brown dun. It is often hard to decifer what you've got without genetic testing.
Oty has also produced a red dun over a chestnut, and what looks like a dark black/brown - but who knows?? Many say the dun gene is dominant, which means you will get some form of dun with any colour mare. The trouble is, when you get to your really dark horses, you often can't see the dun markings.
Most of the photographs on this page are of his offspring while I had him, and one from Taree. If I can get my hands on any photos of others he produced while residing in Taree, I willl put them on the website too. So if anyone has any out there, please email them or post - I would love to see them. I have added the colours (as recorded) of his ancestors to help trace his colour genes. Unfortunately, much of the genetic understanding is quite recent, so many horses have been recorded incorrectly and that can make it hard to follow.
Some websites of interest: