The Responsive Tabs theme gives you a lot of flexibility in selecting fonts and colors. We are all about reducing page weight, so we want to allow people to give people the tools to choose their own branding without necessarily overloading pages with a lot of images.
That said, we recommend you choose one or two fonts and colors and stick with them at most levels of the page. Consider a standout font in the Front Page Highlight area (if you choose to populate it).
Use the colors that speak to you, but we’ve concluded for our own use that softer colors are easier to look at if you are actually reading.