Have you managed to look at the Theme Settings then Color? This is normally there. If not we'd be happy to help you with that if you don't mind sharing your Store's URL here or privately. Cheers!
Thanks for reaching out.
I appreciate the context that you have shared as that is helpful. Using the Debut theme, you can change the the header section color and text color by navigating to the Theme Editor and selecting on the header section. I took a screenshot of my test store to show you the sections I am referring to:
Let me know if you have any additional questions, I would be happy to help out.