I see this question a lot in the forums but since I like to troll them without registering (I hate email spam) I am posting the answer here.
This is for the WordPress Twenty Thirteen (2013) theme.
(Note: change the #FFF to whichever html color code you want)
Now, if you aren’t sure what to do with that code, there are two main options.
- Create a child theme and add it to the style.css file. You can read how and why you should use child themes here.
- Use a custom css plugin and add it to it’s css area. I like jetpack since it has a bunch of useful modules but there are plenty others if you’re not a jetpack fan.
If you haven’t tried twenty thirteen yet, you should give it a look. It’s simple and responsive.