In this map, there are two vocaloids singing, and each one gets a different pair of combo colours for their vocals alongside some other colours for instrumental parts. I cannot for the life of me find out a way to recreate this - thank you! (using Lazer, if it matters)

Unless I'm missing something.. it doesn't seem to be possible with Lazer. On Stable, there's a little drop-down menu appearing once you click on New Combo with an arrow pointing to the left - it'll let you choose whichever combo color you want.

Oh no, guess I'll have to get stable just for the editor.. thank you for your help!

late reply, but if you want to keep using lazer, you can mapping tools and use the combo color studio tool. click "edit externally" from lazer, then select the exported map from mapping tools, and you can manually set combo colors from there.

pretty sure there was a new llazer update where you can do it now

That's true! They did just announce that.

@OP - you may wanna try that now