This is my first test:
This one paints strokes to the viewport while in selection mode (which might be a bad idea, but I wanted to keep the interactivity of the scene behind it). So you should go to Paint Selection mode (the last in the selection tool flyout, or press Q multiple times).
You can set any color, use colors from the preset palette, delete all strokes or delete the last stroke. The drawing is registered as redraw view callback, too, so after you stop drawing, you can pan/zoom/orbit or work on your objects and the drawing will persist as long as the tool is open.
If you close the tool and open it again, the last drawing will be shown again and you can continue drawing. The data will be saved with the MAX file, so you can open a file, start the tool and continue working.
Options to delete a specific (not just the last) stroke could be added later. Same with changing the color of an existing stroke.
Next will be storing a painting per frame, onion skinning and animation playback…