Coloring will come in the first free update after the major release we are working on now. So the major release is the official version 5.0. This is the one all the alpha versions are leading to. This will be in a relatively few months from now and it will be sold for $79 usd for the full license (no subscription). After that we will do the 5.1 with paint and coloring, which will be free for all 5.0 owners.
I am not suggesting you wait with your coloring projects, so in the meantime you can use the excellent export possibilities in Animation Paper – to get your animation over in any other software that you can color in, i.e. any paint package, free or commercial.