It could be a change in seasons or a change in diet. I know my haflinger gets darker in the winter and Rascal just can't make up his mind what shade of chestnut he is. He has gone from very pale almost looking like a dun to a dark liver but I think feed has an effect on his color.
My bay QH gelding goes from medium bay in the summer to almost black in the winter. I think it probably has to do with the seasons. If I can find a before and after picture I will post them. Your gelding is VERY handsome! Posted via Mobile Device
Oxer - is you horse clipped in the recent picture as well? Also your guy looks to be a brown who sun fadded really bad and/or is now getting a much better diet that is improving his coat quality and color.
Cat - Rascal is just plain silly. Lol I really do think his color difference is nutrition linked.
SarahAnn - You guy is also a brown. Pretty typical for browns to go much darker in the winter.