Things You'll Need
Instructions
Load GCFScape and open your "GMod" installation path, locate the Steamapps folder and find the "source materials.gcf" file.
Browse the Half Life 2 model filesin the directory "hl2/materials/models", and right-click to extract and save the model type you wish. Save the model type to a different file on your computer.
Load your photo editing software and open the model file from Step 2.
Edit the model however you desire. Using the coloring options and photo editing tools to recreate the model.
Save the file and and copy it in to your Steam directory with GCFScape. For example, if you made a human male model, you will save the file into the "Steam/steamapps/garrysmod /materials/models/humans/male" directory.
Close GCFScape and load "GMod" to test your new model.