Nav Bar colour

Before you make any modifications to twentyeleven, you need to make a Child Theme. Otherwise, all of your changes will be lost when WP is updated and even more important, you must have a clean copy of the default theme for troubleshooting purposes.

Once you’ve done the above, you’ll need to add this code to your child style.css file:

#access {
    background: -moz-linear-gradient(#252525, #0A0A0A) repeat scroll 0 0 transparent;
}

and change the color codes accordingly.