Hello! Pro comes with 4 color schemes out of the box. If you wish to add additional ones, please follow this page from StudioPress website for a starting point: http://my.studiopress.com/tutorials/color-style-options/.
Once you add your new color scheme, you will need to edit Hello! Pro’s style.css and add new CSS code. You can copy/paste the code blocks pertaining to one of the pre-defined colors and modify according to your branding needs.