To choose brand colors follow the next steps:
Press on Design System under your Website
Click on Colors on the right
3. Set your Brand Colors and click Update
Primary and Secondary colors - are your main Brand Colors, they will help you to attract your customers' attention.
Light - is a lighter version of your Primary color, it will help you to have less contrast.
The first and the last colors - will be used for fonts, so they should be contrast ones.
You can also choose one of the available Color Palettes by clicking on Colors under Website Settings on the right :