A theme repaints the whole app: background, panels, text, borders, menus, the editor, drawings and the paper of handwriting notes. Twenty-four presets ship with Grape, part of Grape Pro, and the accent color stays a separate choice on top of any of them.
The presets
Twelve light themes: Grape, the look the app has always had; Paper, warm and low contrast for long reading; Solarized Light; Catppuccin Latte; Rosé Pine Dawn; GitHub Light; Gruvbox Light; Everforest Light; One Light; Nord Light; Ayu Light; and Flexoki Light.
Twelve dark themes: Grape; Midnight, true black so an OLED screen can switch its pixels off; Nord; Dracula; Catppuccin Mocha; Tokyo Night; Gruvbox Dark; One Dark; Rosé Pine; Solarized Dark; GitHub Dark; and Monokai.
If you know one of these from your code editor, it is the same palette mapped onto Grape.
Picking one
Open Settings and go to Appearance. Appearance at the top is Light, Dark or System. Light theme picks the preset that paints the app while it is light and Dark theme the one that paints it while it is dark; on desktop both grids sit on the same tab, on mobile each has its own page. Every card is a small preview of the theme with a button in your accent color, so you can compare them before choosing one. Picking a card for the other appearance also switches the app to it, so you see what you picked. With Appearance set to System nothing switches: the app keeps following your device and moves between your two picks as it does.
Part of Grape Pro
The themes go with Grape Pro, like the iPhone widgets. On Free or Lifetime the app stays on the Grape theme in both modes: the grids still show every preset so you can see what is there, but none of them can be picked, and the card above them opens the plan page. Appearance, the accent color and text size are not part of this and work on every plan.
Your picks are kept. If a subscription lapses the app goes back to Grape without forgetting them, and the moment Pro is active again the theme you chose comes back on its own.
With the accent color
Every preset works with all seventeen accent colors, so Nord with a blue accent and Paper with amber are both a couple of clicks away.
It follows you
Both picks sync with the rest of your settings, along with the Appearance mode itself, so your phone opens in the theme and mode you chose on your desktop and the other way round.