You are in full-spriteset mode. Press ESC to return to normal single-frame mode.

Here you can choose which sprite set you want to edit. Each row is a full sprite set.

Use the up and down arrow keys to navigate.

Press ENTER or SPACE to start editing a sprite.

While editing you can press I to import a full spriteset from a single file.

Press ESC to go back to the main graphics menu.

If you want to add a new spriteset, go to the last sprite set at the bottom and press the down arrow.

You can change the default palette for a sprite set using the [ and ] keys.

CTRL+C copies a sprite set.
CTRL+V pastes a sprite set.