@MrRoastyToasty Hi. Currently there is no “color swap” paradigm in Pencil2D like in other software, that means it wasn’t considered on the original design but It has been discussed recently by the devs, however I’m not sure if it will be implemented because Pencil2D doesn’t recognize strokes from fills as separate elements just yet.
It has been proposed as well that we have at least a “previous color” functionality to go back to the last color that was used which could cover the use case one normally goes for in software like Flash or Harmony switching between a drawing and erasing color.
On a side note, the problem with having an “erasure” color is that the canvas is actually transparent, and the white background is just like that for visualization purposes, but when you export a transparent PNG you would only see the lines and fills you create.
To change how the background looks (can’t change the color for now) you can go to EDIT > PREFERENCES > GENERAL > Background section and choose the “alpha checkerboard” option (leftmost radial button)
If you want to export with a color card or a painted background you have to either create it in a different layer or import it into Pencil2D.