Customising site colours

Hi, I've bought Clean Education Pro and really love the theme so far, am looking forward to playing with all the options. To start with I'm setting up the site identity and have hit a hurdle with colours - they don't seem to be customisable? Do I need to use css to change the site colours or am I missing something? In - Appearance / theme / customise / colours - there is only the option to change the colour theme from dark to light. And then there is a list of things that can be changed but it's just a list - no places to put custom colours etc..... I'm feeling really stupid! Thanks Kate