https://retropie.org.uk/docs/Colecovision/ sends me to
https://github.com/libretro/blueMSX-libretro and then
https://sourceforge.net/p/bluemsx/code/HEAD/tree/trunk/blueMSX/Make/blueMSXlite/
and I'm getting lost at the moment. I'm going to have another go at all this when I'm not so tired. Thank you for the pointers, much appreciated.