Can I create my own color theme?

Yes. Alongside the seven preset themes, Premium lets you build your own — pick your accent, background and task colors, and Tweek saves both a light and a dark version of it. Your custom theme follows your account, so it is there on all your devices.

1. Click the initials icon in the upper right corner
2. Go to Settings → Appearance
3. Under Custom themes, create a new theme and adjust the colors

Three preset themes are free. The other presets, and any custom theme, need Premium.