[souprock]

Yep. Unless you check the gonads and the DNA on both sides, any explanation will be uncertain.

I note that birds use the WZ sex system, which is like the opposite of the mammalian XY sex system. Males are ZZ. Selective silencing of genes on the Z chromosome for dosage compensation could cause spacial variation across the body. We see something like this in the XY sex system with Barr bodies, leading to coloration differences such as those of the calico cat.

It's also possible to have a plain old male-male chimera, or a plain old mutation, with the cells in one part failing to produce the proper color.