The Zero WordPress theme includes tons of easy to use options to customize the design of your site. Most of your theme options can be found in the live WordPress theme customizer. Zero uses only native WordPress functions, os you should be familiar with the way the Customizer looks and works.
Simply navigate to Appearance > Customize to make changes to the design of your website.
Here you will find lots of options to define different elements of the theme.
The styling tab has built-in color pickers that make customizing the look of your website easy.