From backend admin > Site > Template Manager... select the radio button next to the template name > Edit HTML >
Code:
// *************************************************
// Change this variable to switch the default color-scheme
// *************************************************
$primary_style = "blue"; // blue | light | red | burgundy | coffee | mint | lime | orange | highc-1 | highc-2
Change "blue" to your desired default > save
(the file (<website>/templates/rt_rokwebify/index.php) must be writeable)