Generated Gcode doesn't set extruder_colour when it is set to filament color

[PinkPandaKatie]

Description of the bug

If I go to Printers -> Extruder # -> Extruder Color, and click "Reset to Filament Color" for all of the extruders, then the generated Gcode contains a blank extruder_colour value. This causes the Filament Mapping screen to not show the colors for the filaments.

PrusaSlicer's Gcode viewer is still able to view the filaments because it looks at the filament_colour in the Print Metadata block, but the printer can only look at the Printer Metadata block which only contains extruder_colour, since Print Metadata is Deflate compressed.

Project file & How to reproduce

1. Go to Printers -> Extruder # -> Extruder Color and click "Reset to Filament Color" for all extruders
2. Go to Filaments and set up two or more user presets with different colors.
3. Slice a multi-color print that uses these filaments.
4. Export the Gcode and examine the header. Note that extruder_colour is blank.

Checklist of files included above

• [X] Project file
• [X] Screenshot

Version of PrusaSlicer

2.8.0

Operating system

Ubuntu 22.04

Printer model

MK4+MMU3

[PinkPandaKatie]

Project file upload failed the first time. Here it is:

screwtray-project.zip

[PinkPandaKatie]

I don't know where the best place to correct this would be. One possible solution would be to add "filament_colour" to the list of keys copied to the printer metadata block in GCodeGenerator::_do_export, then have the printer firmware check filament_colour if the corresponding extruder_colour is blank. It could also probably be copied to extruder_colour in that function, but that seems like a hack.

[lordofhyphens]

It's not a code fix, but it looks like at least HappyHare's preprocessor will find the correct values if you put in a fake extruder_colour = entry in your start gcode that has a ; separated [filament_colour_0];[filament_color_1]...[filament_colour_n]