He's got a lot of the mealy going on, and in fact underneath his tummy he is pure white (although now I think about it, I think he may have a bit of a black line on his tummy, he grows really long black hairs among the white in winter. But I will have to check to be sure.)
But mealy-ness is standard for mules right?
As you can see on the pic, the top third of his neck is much darker than his body colour, and he has dark hair coming down his shoulder from his whither (but no stripes).
He has a dorsal stripe, a pretty dark, distinct one, which you can't see in the photo unfortunately... is this pretty standard for mules to have?
He has black points: black to the knee, black main and tail, ears are not black but rimmed in black.
Are all these things just the normal 'mule' expression of bay? Or do mules express colours in a similar way to horses?