He is gray, most gray horses will get a red tinge out in the sun. I have seen some gray horses that are left out all summer and turn the ugliest muddy brown but then when they are clipped they are as silver as a new dime. I often get blasted for my firm insistance that gray and black horses should be stalled or kept out of the sun during the day and put out to pasture in the evening and at night to perserve their color.
Here is why I made my guess. Coco Puffs is a known silver dapply varnish roan appy with a blanket...and your mare looks to be the same color. Coco's blanket shows better at different times of the year.
If he were Grey chances are he would be white by now. Grey also does not follow the pattern this horse has- when mixed with the "Varnish" pattern it tends to intermingle and send it almost white much quicker. This horse is not Grey. As said, he is Silver + , probably, Varnish, + Blanket, of course!!