He's also much bigger and broader, almost hulking, than Mario and all of his 'clothing' are actually part of his body, which explains why they also change in appearance and size when he shapeshifts.
In his default appearance, MX's skin is pale white, his mustache, shirt, hair, shoes and eyes are black, and his hat and overalls are a darker shade of red than the actual Mario's. game, with dark tan skin, a red hat and overalls, and a brown-green shirt with matching mustache and shoes. When disguised, MX looks exactly like Mario does in the original Super Mario Bros.