My imperial horse used to be white. It now looks like it's covered in soot and is a light greyish color. Why? Is this on purpose or was it accidentally darkened too much after adding more fur?
Are you sure that's your Imperial horse? It sounds like you have a different horse equipped. My Imperial horse still has white fur. However, there is another horse that was purchasable from the crown store that looks like the horse you described. I suggest you go into your Collections and make sure you have the Imperial horse equipped.
Looks like your character is in the dark. Try looking at the horse when in sunlight. If it still looks greyish, could be a graphical issue on your end. The horse still looks white for me.
"You have spirit in your eyes. I may take those from you when this is over."