Bays don't have a real dorsal stripe, but they can have counter-shading that looks like a dorsal. But it's smudgy, and the edges are very well defined. A real dorsal looks like it was drawn with a marker. Posted via Mobile Device
Bays do not have dorsal stripes caused by the dun gene. If the dun gene is present, the horse is no longer a bay, but instead they are a bay dun.
However - bays can have dorsal stripes. It is caused by something else - counter shading possibly - but it is still called a dorsal stripe. Dorsal stripes are not exclusive to dun horses, and they are called the same no matter what is causing them.
This guy cannot possibly be dun - he is a registered Arabian. As you can see, his dorsal is clean and crisp.
I've had two purebred Arabians with dorsal stripes, shoulder barring, and tiger striping on their legs and the ears (which one passed onto her colt). All just counter shading.
I have a light chestnut that almost looks like a red dun but since she's purebred, that's not an option. LOL