What color will our colt turn?

ok my mare had a mule colt and he was born solid black but now that he is a month old hes way lighter now hes about a light brownish black color but hes getting really light like a dun color on his but and and his muzzle and he has zebra stripes starting to show up on his knees im not an expert but ive never seen a mule with zebra stripes unless it was dun or or buckskin almost brown color