I would think any rich warm, such as sienna, ochre, cadmium red, cadmium yellow would be a good start. You’d have to tone it down with a compliment, though, or it wouldn’t look natural. I’d probably start with the ochre and add a bit of cad red and sienna.

[FONT=Palatino Linotype]Linda - C&C always welcome
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Naples yellow is a wonderful colour for the lights (mixed with a touch of white). I use Liquitex heavy bodied acrylics and they have a terrific colour called quinacridone burnt orange and this mixed with raw sienna is fantastic.
Like Einion says, a photo would make it easier to give advice.

I don’t paint horses, all those sound like good suggestions. But also consider the environment. The lighting will change everything, as you can see in your samples – is it summer? winter? evening? You may well know all this – but I thought I’d chime in.

I’ll take a stab at it. Using the top picture as an example, I’s start with some yellow ochre mixed with as much titanium white as you need for the lighter areas. As the color deepens you can add some burnt sienna and some burnt umber. In the darkest shadowed areas, such under the belly, the back part of the rump, etc. you need a dark, dark, somewhat cooler color so I’d mix some ultramarine blue and burnt umber. You can make it lean more to the cool side by adding more ultramarine blue, or lean toward the warm by using more of the burnt umber. The gray of the muzzle area is a more neutral gray which you can get by adding enough white to the dark shadow mixture until it looks right. The mane should be a creamy light color, not pure white. You can add touches of other colors, as needed, but I hope that’s a start.

I notice in the next to last photo, this horse (beautiful, by the way!) has some bright yellow highlights in certain areas that would benefit from an intense yellow, like cadmium yellow light, and even touches of orange.

The bottom photo is very different and more subtle. I’m thinking some raw sienna and naples yellow mixed with white, of course, some darker and cooler mixes where needed.

I’m sure others will have lots of suggestions.

Beverly