Is it possible to give a

TextDecoration

a separate colour from the text being decorated? TextDecoration

Not possible.

Is it something that would be straightforward to implement or would be quite involved? I don't know if you allow contributions or anything for that kind of thing 😅

I don't know the solution so i dont know if it is straight forward to implement. It might be involved since it has to be performant, handle bidi cases and all languages. I believe platform didn't allow us to implement it in a straightforward way.