Hi Ethan, thanks for asking!
There’s a good reason why the painting tools (including bucket fill tool) doesn’t work. It’s because we haven’t implemented them in yet. 😉 Earlier in development of Animation Paper, we had a lot of greyed out menu items and tools, that was to come. We did this so people could get a view on what we where planning on doing. Now that the paint tools are more or less the only thing missing, I know it must be more confusing than informative. And that’s why, in the next release (Alpha 8) the whole Paint menu is hidden.
Paint and coloring are the very first features to be implemented after we have finalised the official v5.0 release. Paint/coloring will be a free 5.1 update.
To color you animation in the current situation, you can export your animation and color them elsewhere (like in Photoshop or the free Krita or whatever paint package you might have available). You can export as a sequence of PNG frames with numbering showing where any clones might be and layer information. A more advanced way of exporting is using OCA (Open Cell Animation), that enables you to export to multiple other software and transfer information on timing, layers, FPS, etc. More about OCA here: https://animationpaper.com/animation-paper-oca-export-for-pc/
Let me know if you have additional questions!
Thanks,
Niels