Post Categories Block
The Post Categories Block allows you to display a list of the Post’s Categories. Each Category is separated by a simple vertical bar divider, and will include a link to that individual Category Archive page on your site. This block will only work within Posts (not Pages), and will be more useful once you can edit your Theme’s templates.
Once you've added the block, there are further options available in the Settings Sidebar including an option to select the font size, color and background color.