Chestnut is one of the foundation colours on which other colours are made. It is a colour that is usually orange in appearance, although it can range from very dark liver through red to a light orange colour, under names for the shades such as Liver Chestnut. Chestnut horses have legs that are the same colour as the body - they do not have black points, though of course they may have white markings on their legs. The mane & tail can range in colour from white or flaxen to very dark – sometimes so dark they can actually look almost black. The darker shades of Chestnut can sometimes be confused with other colours, however even these darker colours will retain a reddish tint somewhere on the horses body.

One of the colours that a dark Chestnut may be confused with is the darker shades of Silver Dapple – here the hint is in the lower legs & mane & tail. In a Chestnut, they will have a reddish tinge, and the mane & tail may also have an almost ‘sunburned’ look which will be absent in a Silver Dapple. If in doubt, a genetic test for red factor will claify things – if the test comes back as ‘E’ then the horse could be Silver Dapple, if it comes back as ‘e’ then the horse has a Chestnut base.

Sometimes with lighter shades of Chestnut, you can get a lighter mane & tail, elbows & underbelly – this is caused by modifying genes called Pangare (Mealy) and/or Flaxen – Flaxen itself will only affect horses with a red base. At this point it is believed by scientists that the Silver gene has no physical effect on Chestnut based horses, and cannot dilute red pigment. The red of the Chestnut colour is caused by a pigment called Pheomelanin.

Genetically speaking, a Chestnut horse is a horse whose copy of the gene that produces black hair is "switched off". The gene that produces black hair is symbolised by the letter 'E’. As Chestnut horses do not have a "switched on" copy of this gene, they may be referred to as 'ee' horses - the lower-case letter is used to show that the gene is "switched off". For Chestnut to be displayed as a colour, the horse must have two doses of the ‘e’ gene. Since Chestnut is a recessive gene, it can be ‘hidden’, even for many generations, and may therefore seem to appear out of nowhere quite unexpectedly in foals. It may be necessary to go back several generations to find the responsible gene. It is possible to test Black based horses to see if they have a recessive Chestnut gene, which may allow you to predict your horses genes which it may pass on.

A Chestnut put to a Chestnut will always produce a Chestnut foal. Chestnut to Black or Bay or Brown may produce a Brown, Bay, Black or Chestnut foal - though Bay and Brown seems unlikely, it is possible, as Bay and Brown does not show on a chestnut horse, hence can be ‘hidden’.

Red or Chestnut based colors include:
• Chestnut diluted by Dun is called Chestnut Dun or Red Dun – sometimes paler shades are inaccurately called Cream Dun in Shetland circles which may lead them to become confused with other shades like Palomino Dun (Dunalino)
• Chestnut diluted by Cream is called Palomino when there is one copy of the Cream gene and Cremello when there are two copies of the Cream gene – Cremello is the only modified version of Chestnut that appears differently in single or double quantities
• Chestnut with the Silver gene does not show physically, but is called Chestnut, Silver Carrier
• Chestnut diluted by the Champagne gene is called Gold Champagne
• Chestnut modified by the Roan gene is called Chestnut Roan, Red Roan or Strawberry Roan