In a nutshell, you define different materials while modeling, then change those definitions to a variable parameter in the GDL script.
*******
When you create your object, define a different material for each part of the object that you would like to be able to adjust individually.
For example, a chair with different materials for the legs, seat, and back. Assign Paint-01 to legs, Paint-02 to seat, and Paint-03 to back.
Save object as editable GDL object.
Place the object in your plan, select it, the open object using CTRL+SHIFT+O
Create a new material parameter for each item, in this case 3 of them. For this example, use the variables 'leg_mat', 'seat_mat' and 'back_mat' and choose a default material for each.
Then open the 3D script, use the 'search and replace text' command to replace "Paint-01" (include quotes since it is not a variable) with leg_mat (no quotes around variables), "Paint-02" with seat_mat and "Paint-03" with back_mat.
Hope that helps ~
AC 6-27 - Intel i9-9900K - RTX3090 - Windows 11 - 64GB RAM