He at all,
I’m try rhino 6 on windows, wit a little assembly .step format.
I assign 12 level, every one with 2/8 components, and every level a specific materials.
The render prewiew show my only predefined colour (white) and no one of material coluer that I can see on my view during the render setting operations.
I not use mesh or texture, and not use different faces colour. Do not use blocks, only material and colour setting on every level on solid comp origin by .step assembly.