I feel like a broken record, but the Fly Turtle is my choice.
Suggest you do a search. This comes up approximately once a week, every week, from March to September. Try going into the Advanced Search menu, searching for the phrase "fly sheet", choose "Search Titles Only", and near the bottom choose "Show Threads" instead of Show Posts. You'll be DRIPPING in threads, literally dozens of them on this exact topic.
If your only concern is coat fading, I don't think a fly sheet would be the way to go. Reason being, they do sweat under them. There are other options that won't inhibit air circulation.
Do't get me wrong, I am all for fly sheets on horses who need the protection from flies. I have one who lives in his. But in the heat, he does get sweaty around the shoulders and chest, moreso than he would without the sheet. BUT, it's either this or have no hair from the shoulders forward. Literally.
I have a Fly Turtle for him. It's awesome, though not indestructible on a bottom-of-the-pecking-order wussy gelding. I have had it replaced once already. They do stand behind their warranty though, at least for one replacement!
If it were my horse, I would try the SmartOmega3 and a coat sunscreen first.
The supplement is absolutely worth a try. My horses already had their full summer coats when I started it, and I started noticing major changes within a couple of weeks. After a month for sure, it was like WOW. I could not believe the shine. http://www.hphoofcare.com/Conformation.jpg She grew in dapples, which she has never had before.
Fly Turtle! Most amazing product I have found. The chiro was out recently and raved about the fit. Said it was the first blanket she'd ever seen that really allowed freedom of movement. I have mine on a fiesty 2yo (with bug issues). No rips, snags, etc and she wears it 24/7 in pasture. It never slips, turns, truly amazing. Lightweight woven fishing line. It was 103 today and no sweat underneath (it was breezy though). A bit pricey at 135, but includes neck cover, replacement straps and a 1 year warranty.
Do not toy with the dragon, for you are crunchy and good with ketchup!