picking a theme

hi. have begun the process of setting up a website/blog, and am seeking someone’s advice in picking a theme … i am too computer illiterate to be able to tell the difference between the technical aspects of each theme and what each offers other than what i see visually through preview. most important aspect of my blog would be the ability to have the background colors alternate in the main text content area, and that those colors should be light in color. any suggestions as to which template to choose? the only other requirement is that the template be able to support small ads along the side or bottom. thank you!