You could try to find a spray that prevents it. It works wonders, I just can't think of the brand that I use!
We only turn out at night to keep from sunbleaching. So I would say light sun or fly sheets
Fly sheets are good and will help. You can also try using a color enhansing shampoo. My friend gives that to her bay and it really helps throughout the summer.
Fly sheets help keep the coat from sun bleaching and help the coat darken. Good feed is very important also.
Good feed is always important. Make sure he is getting the proper omegas. You can slap find sheets with uv protection.
Fly sheet but make sure it has UV protection. Weatherbeta is my fav