Stackup colors could affect 3D viewer or exported models

Context

Change the board physical stackup, the information appear to right exported to the *.grbjob file, second https://www.ucamco.com/files/downloads/file_en/356/the-gerber-job-format-specification-technical-manual_en.pdf. Even change the Mask and Silk colors are there but is doesn't have any effect on board 3D viewer or exported STEP / VRML / ... files.

Propose

Use the information (color, tickness, ...) of the Board Setup >> Physical Stackup to render the 3D image of the board and also for the exported STEP (and others) of the complete board.

This will make the visualization and exported models more authentic.

KiCad Version

Application: Pcbnew

Version: 5.99.0-unknown-b993a2969~91~ubuntu20.04.1, release build

Libraries:
	wxWidgets 3.0.4

Platform: Linux 5.4.0-47-generic x86_64, 64 bit, Little endian, wxGTK

	wxWidgets: 3.0.4 (wchar_t,wx containers,compatible with 2.8) GTK+ 3.24
	Boost: 1.71.0
	OCE: 6.9.1
	Curl: 7.68.0
	ngspice: 31
	Compiler: GCC 9.3.0 with C++ ABI 1013

Build settings:
	KICAD_SCRIPTING=ON
	KICAD_SCRIPTING_MODULES=ON
	KICAD_SCRIPTING_PYTHON3=ON
	KICAD_SCRIPTING_WXPYTHON=ON
	KICAD_SCRIPTING_WXPYTHON_PHOENIX=ON
	KICAD_SCRIPTING_ACTION_MENU=ON
	BUILD_GITHUB_PLUGIN=ON
	KICAD_USE_OCE=ON
	KICAD_SPICE=ON