Modified for multi-material. All colors in the same layer.
Either import individual .stl's and align them, or import .3mf and pick "Import 3D models" (should open aligned models, assigned to extruder colors)

!!! ensure "Purging volume multiplier" is set to at least 200%. Otherwise there is no guarantee white/yellow will be pure color after transitioning from black.
Other option is to use M600 in "Tool change G-Code" macro. Filaments must be changed manually, but allow for checking correct color.
In case of MMU, add also Z-lift and tool change prior M600; e.g. via macro:

Top layer is set for ironing to minimize garbage from sponge growing on the holder..

Prusa

i3 MK3 MMU 2

No

No

0.2

N/A

had blue and brown in PLA only, so mixed it with rest of PETG