Pale Horse

http://www.solaris-sport-horses.co.uk/perlino_akhal_teke_stallion.shtml

This, I think, is what a "pale horse" would refer to, Kambarbay at this
link. Cremello is a similar color. This turns up in a lot of breeds with
Turkic blood in their foundation ancestors, incl. the American Saddlebred
I think, and some others. At the time Revelation was written, many would
know of these horses in the hands of destructive Scythian tribes, ancestors
of the Turk peoples. So one would get the picture of a massacre happy
rider who was pretty invincible and not outwittable like the rider on the
black horse, who related to economic issues and probably oil, the same
color as the horse.

Medieval artists sometimes painted this horse a green color, for lack
of any idea what it might be.