I'm creating a character that has paint-like footsteps, how would I be able to use dynamic paint to create a paint splatter effect while the character is walking?

Thats a tricky one. I'd use a two step approach to get this result. 

First, I'd use the feet of the character as one dynamic paint brush. This will take care of outlining the footprint.

Second, I'd add a particle system to the bottom of the foot and use the particles as another dynamic paint brush. This way, it adds a dripping effect that may replicate a paint splatter. 

Thank you!