From your Paper Settings Dashboard, click Layout & appearance, then Look & feel, then Font scheme to view your font settings.
You can change the font size and color for your Paper title, the font and size for the Article title and text.
Special note for publishers using the Paper.li News Page App (on a WIX site)
Using the Paper.li News Page App on your WIX site? All layout and color controls are found by accessing your WIX page settings. Click anywhere on the body of your Newspaper to see Settings button, shown below. From there, you can edit the text color, choose a font, and choose a general color scheme.