I'd like to point your attention to Magellan. Magellan is a map editor targeting the Texas Instruments TI-99/4A home computer or more generally speaking the TMS9918 VDP.
Codex (the programmer) did a great job and Magellan already sports some nice features in the current version.
There is no specific colecovision output format at this time, that is why I'm hoping someone could chime in to help with the specs for that.
However, Magellan is already able to export binary files. The file format is documented, so a Z80 player could easily be written, I hope
Check here for the details.
Please note this is still a work in progress.
The TI-99/4A and Colecovision communities aren't that large, that is why a joined effort could make sense.
We can always use some more ideas for new features, etc.














