Horse breeders interchange the terms sorrel and chestnut to describe red horses.
And by breeding two reds together you will only get red foals. Many modifying genes produce various shades of red horses due to unknown modifiers, but others like the blond sorrel or liver chestnut can be explained. Then there are the genes we can all recognize that affect the red coat. The dun gene produces lineback red duns. The dun gene is very similar to the cremello gene in that it dilutes the coat color but not the point color, it produces lineback duns.