It took me some time to figure it out — I even had to ask for support — but now I’ve got the hang of it.
If you think there’s too much black in the free WordPress theme Twenty Fourteen, you can change it for free.
Dashboard > Appearance > Custom Design. Click ‘Preview colours for free’. There are featured color schemes. Choose one of those and save. If you’re not happy with the featured schemes, you’re out of luck, unless you want to pay $30. You can choose your own colours and you’ll see in the preview how nice it looks, but you can’t save. Hah!