File:Leather horse armor.png

Summary
The leather horse armor icon is in the game's assets, but since the armor can be dyed, the color for the decorations is defined in the game code. The color for horse armor is defined in the HorseArmorItem::getColor function; more specifically, the default color is defined in this section of code: http://i.imgur.com/AjK7xmF.png

What that code does is define 4 32-bit floats with  storing the red,   storing the green,   storing the blue, and   storing the alpha. Converting those values to a floating point value gives an RGBA color of (0.627451, 0.396078, 0.250980, 1.0), or (160, 101, 64, 255) when converted to 8-bit integers. The overlay color is applied using shaders by mixing overlay color with the icon color with the alpha channel controlling the mixing. Applying the same operations in a photo editor gives the default icon for leather horse armor.