Would echo the fly rug, mine wear a Rambo Sweet Itch Hoodie (we are in the flatlands with ponds and dykes, and the flies have FANGS), and the material is so dense the sun does not bleach my Horses' coats.
Fly rug with UV reflective material. I got the Mark Todd one for last summer and it made a big difference. Summer 2012 my horse looked orange but summer 2013 was much better with the rug on every day. I think it made him cooler in temperature as well.