Adding color or images into the background within a column?

Hi, I just started using the free “Blaskan” theme provided in the available themes section.

I was wondering if there was a way to add color in the main text column section of posts and pages? I would like to maintain a clean white background / backdrop, but perhaps add in just a hint of color or even a low opacity image behind the text on my pages.

Is there a way to do this by modifying the CSS? Thanks so much for any assistance.