Is he under winter coat? If he is then it may be hidden right now. I do see some tiger striping around the legs and a dorsal stripe... I'd have thought dun if I saw him right off but maybe the brindle is hidden under his winter coat...?
Pfft. I have yet to see one of those that consistently has that.
There is someone who breeds "seasonal" brindles. I have yet to see one of the foals have that "seasonal" brindling or any brindling at all. The word brindle with the coat color garners them lots of cash though as people can and do dump the money on it because they think they are getting an uber rare color.