Within Teamwork, you can set a custom color theme that will show in the header area of your site.
Click your profile icon in the top right of your site and select Settings from the dropdown menu.
In the settings area, go to the Color Theme subsection.
You can choose one of the preset colors on the left or set a custom color theme.
When setting a custom color, you can either enter a hexcode value or use the color palette.
When you click any color, you will see a preview of that in your site header. Click Save Changes to update your site theme.
For more information, see: General Settings