Ponies are often described as light bay, dark bay, red chestnut, pale palomino, etc. The differences in those is called shade.
Shade differences can happen with any color. Flaxen, mealy, and sooty can modify a pony's color but that can't explain all of the differences which leaves shade. There's been a lot of recent interest in shade but little is known about any genetic mechanisms yet. A pony of particular shade will regularly produce offspring of a shade different from themselves. There was a study that indicated that bays with one copy of extension will generally be lighter than a bay with two copies. Genetic components to color shades in dogs have been found.
Shade differences can happen with any color. Flaxen, mealy, and sooty can modify a pony's color but that can't explain all of the differences which leaves shade. There's been a lot of recent interest in shade but little is known about any genetic mechanisms yet. A pony of particular shade will regularly produce offspring of a shade different from themselves. There was a study that indicated that bays with one copy of extension will generally be lighter than a bay with two copies. Genetic components to color shades in dogs have been found.