I ADORE chestnut horses. I'm in love with them. I know you shouldn't fall in love with a horse based solely on it's colour, but my heart skips a beat when I see a chestnut horse.
There are many different shades of chestnut, and I've found it frustating that many people name the shades but don't provide picture references to explain what colour they mean by each name. Now, I know this is very difficult to do: after all, there are so many different shades that sometimes it's hard to tell which category a colour would fall into. There are also different shades defined by different breed registries.
What I've decided to do is make a very basic, general colour guide to various shades of chestnut. There are more, like black chestnut, but these are the most common.
Chestnut: a chestnut horse is a red based horse. It's colour can range anywhere from so light they look golden to so dark they appear almost black, but the key factor of chestnuts is that they don't have any black hairs on their bodies. Their manes and tail can be several shades lighter or darker than their body colours, and they have grey around their nostrils, lips and eyes, unless masked by white markings/other modifying genes. They also tend to get lighter towards their hooves, unless these hairs are covered by white markings.
Golden/Light chestnut
The palest chestnut shade. These horses have quite golden-orange or pale coats.
Standard chestnut
The most common colour, and the shade that most people think of when they hear the term 'chestnut'. Sometimes called 'sorrel'. The horse is a rich coppery orange colour.
Red Chestnut
Not always distinguished as a separate shade, but one that I like to refer to separately from standard chestnut. These horses have a much more reddish body colour, like cinnamon.
Liver/Dark chestnut
These horses tend to have a darker, more brownish colouration to their coats than standard or red chestnuts. As the name implies, they're often a reddish brown colour, like liver.
Flaxen chestnut
These horses have a blond, or flaxen, mane and tail. Their body shade ranges from light to red chestnut. The flaxen can range from almost white to rich yellow/blond.
Liver flaxen chestnut
Dark or liver chestnut, with a blond/flaxen mane and tail.
Sooty chestnut
Whilst this horse might just be a dark maned liver chestnut, the brown coat and the dark, almost black mane and tail are sometimes indicative of a sooty chestnut, that is a chestnut carrying the sooty gene. Sooty may also have counter shading/dark areas on the top of it's body/back.
Flaxen pangare chestnut
The pangare gene lightens the soft areas of the horse's body, often affecting the legs, belly, nose and hair around the eyes. The degree of lightening varies between horse. Pangare chestnuts also normally have blonde/flaxen manes and tails. This colour can often be mistaken for palomino, but it is not. The horse doesn't carry the dilute gene. Most famously seen in Haflingers and Belgian drafts
Panagre chestnut
Much rarer than the flaxen pangare, this horse only have lightening on the soft parts of it's body, not it's mane and tail.
All of these horses were referenced from photographs of real horses and ponies.
Renders (c) me
Golden/light chestnut (c) http://www.whitehorseproductions.com/ecg_basics1.html
Standard chestnut (c) http://www.everything-dream-horse.com/images/chestnut-horse-a.jpg
Red chestnut (c) http://www.examiner.com/images/blog/EXID17191/images/chestnut_horse.jpg
Liver chestnut (c) http://www.atspringhill.co.uk/cj.jpg
Flaxen chestnut (c) http://www.whitehorseproductions.com/ecg_basics1.html
Liver flaxen chestnut (c) http://www.morgancolors.com/mocomochrome.jpg
Sooty chestnut (c) http://www.horse-genetics.com/chestnut-horses.html
Flaxen pangare chestnut (c) http://images1.fanpop.com/images/image_uploads/Haflinger-horses-1256940_400_267.jpg
Pangare chestnut (c) http://www.theequinest.com/colors/modifiers/pangare/