By default, this currently cannot be done with the Combo chart object, the colors are fixed. There may be a expression type approach to get this done, but the work involved may not be worth it. Our R&D team is aware of this and other style improvements and I have logged your request in our system.
let us know how else we can help you.
Please mark the appropriate replies as CORRECT / HELPFUL so our team and other members know that your question(s) has been answered to your satisfaction.