If you're wanting all black, Chimacum is a great option. It's Comfy-Fit harness, but they are currently not able to do custom colours.
If you're able, please find out what kind of collar your animal likes pulling in best. That could change with your vehicle. Mine likes the Euro-collar best. Some people poo-poo the Euro-collars, but he really likes his. We also use a K-cart with all the bells and whistles.
The biggest piece I'd recommend for donkey-specific harness is to get a bridle with a clip at the crownpiece so that you don't have to pull ears through it. Much more comfortable.
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