Currently you can only use and customize the default 6 Chart series colors (Kendo Colors Series A, B,C,D,E and F) using ThemeBuilder. Any additional ones needs to be defined in the component code. This is not ideal if you want to manage all colors from ThemeBuilder.
The request to have either have the ability to add new Chart series colors in the ThemeBuilder which you can use with the chart or have more variables exposed at the beginning 25+