Pawn wounds are currently hardcoded for the three vanilla flesh types. Using custom flesh types will result in an error and will fall back to normal flesh type (red blood graphic).
Suggestion is to allow modders to add new flesh types with customizable color and/or graphics via XML.
Or at the very least, remove the error and disable wound rendering if using a custom flesh type.
(https://i.imgur.com/UevIgIN.png)
Common error, a bit annoying, only TiberiumRim has it from my mods though.