Changing Colors in Your Drupal Theme
In the previous version of Drupal, to change the colors your theme used you had to open the style.css file on a desktop computer, make the changes, and then upload the altered style.css to the Drupal/sites/all/themes/drupalfordummies folder on your web server. It's much improved now, with most themes having a built-in interface to change color settings. For example, you can manipulate the colors in the Garland theme as follows:
Go to Appearances.
Select Garland as the default theme.
Click the Settings link next to Garland.
This opens the settings page.
Change the setting in the Color Set drop-down list.
In the example, Citrus Blast was selected. This changes the theme's colors. Scroll down to see a preview.
Change individual colors on your site.
To do this, click the section you wish to change and clicking the color wheel to the right.
Play around with the settings.
When you’re happy with the result click Save Configuration.
If you know the hexadecimal value for the color you want to assign, you can also change colors by typing the hex values into the text boxes.