Derma Wax is a transparent wax. If you want the wax to have the proper colour when used more thickly to create a deformation (a large lump, for instance), you can do this using Grimas Crème Make-up Pure or Camouflage Make-up Pure. Powder off with a make-up sponge with Grimas Transparent Powder to matt and fix it, then turn the sponge over and continue dabbing with the clean side until the excess powder has been removed.
To create an 'open wound', the Derma Wax construction has to be 'cut open' with the sharp side of a Derma Wax spatula. Lubricate the tip of the spatula with a little bit of Cleansing Cream. This will allow the spatula to slide more easily through the Derma Wax, preventing it from sticking to the spatula.
Opening the wound edges up allows you to create a tattered effect. Raise the 'wound edges' using a Derma Wax spatula, lightly lubricated with Cleansing Cream. Do this carefully.
Colouring: To add a suggestion of depth to the 'wound', colour the bottom of the wound using black make-up. Then you colour the inner side of the wound with dark red make-up (Grimas Water Make-up Pure or Crème Make-up Pure).