The Blender template I created does not handle transparent parts with decoration. Even if they are not that common, it is good to know how to set up the materials manually for them.

1. Alter the decoration file in an image editor. Only keep solid areas.
   

2. Replace the material of the part by the following:
   

Add a Transparent custom shader and set:

• Color hex value as per the value found in the colours.py script
• Scale value to match the Solid shader

Add a Mix Shader node

• Link the transparent shader to the first Shader input and the solid shader to the second Shader input.
• Link Alpha output of Image Texture to the Fac input