@qmc2 Thanks. It launches the game from the software list after removing the colon in ~/.qmc2/mame-xml-cache.db in the coleco (and did it for colecop too) row.

I haven't had much time to look but it appears that the issue is rooted here, src/devices/bus/coleco/exp.h:90:
Code:
	virtual const char *image_interface() const override { return ":coleco_cart"; }


Comparing it similarly like you did to src/devices/bus/nes/nes_slot.h:364:
Code:
	virtual const char *image_interface() const override { return "nes_cart"; }