Thanks for that, although I couldn’t get it to work, it did lead me down a series of rabbit holes. I ended up splitting the (original) models in F360, importing the STLs as one, splitting them to objects, assigning a coloured filament to one, then joining them back up.
It did leave the model less than perfect where for some reason where they join it added a layer on top, but I’m sure with a bit more experimentation, I can fix that.