I think it would be helpful to have 2 more options in the background settings:
The simplest would be to add an option that allows the user to select colors for the background that “pulse” back and forth.
The user should also be able to select how fast they pulse.
This makes it easier for the user to see the difference between transparent background and the sprite. There should be a text box that lets the user input how long it takes for a full cycle of textures to complete.
The second goal, (while extremely useful, seems harder to program) is to allow the user to upload a gif or video file to act as the background. This would make it easier for the user to see what their sprite looks like against a backdrop. I assume my former suggestion is more easily achievable, but please consider this because it may make this software unique in the landscape of pixel software.