?page background doesn't go back to the default black when coming back from a passage with a gradient or striped ?page background.
Starting from a passage with the default Harlowe appearance (white text on black background), if we go to another passage whose ?page has been enchanted to have a gradient or striped background, and then come back to the initial passage, using either a link or the undo button, or go to another passage with no enchantments, the page's background appears white, instead of the expected black. Since the text reverts back to white as expected, it becomes illegible. Enchanting a page to have a flat coloured background doesn't cause any issues. In fact, going to a page with a flat coloured background "fixes" the white background issue.
A simple example story: Background_Issue.html