you can do this by setting the background to black, then lock it. When you click generate again, the subsequent palettes will then take the dark background into

you can do this by setting the background to black, then lock it. When you click generate again, the subsequent palettes will then take the dark background into account. there's also a dark mode preset in the (gear icon) menu. I concede this is not totally obvious just from the UX, maybe it needs a tutorial or something...