How to Adjust STL Surface Color?
If the PDF appears as pure saturated white surface without shading, tryt the following steps:
1. Add File or drag & drop the STL file into the input menu
2. Select the STL file row, enable the options checkbox, select the STL interface.
3. Then go the Interface Settings tab, and the STL interface sub-panel.
4. Near the top of the menu is a file selector, pull down to pick one of the STL files at a time.
5. Then near the bottom of this panel there should be STL Interface sub-menu.
6. The color selector can be set for the color for the individual file.
7. If more than one STL merged, select another STL, and set color as before.
This is a special case for STL, most other file types you can use the Visual Effects menu. This should allow you to set up distinctive part surface colors.