Yes you can.
To make changes to your website header, open your WEBSITE module.
Within the menu at the top, click on the HEADER & FOOTER>HEADER.
This will bring up your header options. The style highlighted in blue is your current selected header.
To edit the colour of your header, click the edit STYLES button located on the selected header.
In this menu, click on the HEADER. Here you can change the colour and the Opacity of your header. Simply click in the box to bring up your colour choices.
Click SAVE CHANGES.