Develop web parts around a fixed defined colour palette might helps you to achieve the goal. Why not write a web part that used the SharePoint Design defined colours instead. This way all custom web part doesn't look like aliens on a page and smoothly integrate to the overall user experience.
SharePoint Framework offers a way to make web parts with colours defined outside of the web part context and reuse the design that already is applied on a page.
Learn what stepping stones exist using SharePoint theming in web parts. This session shows you how to use the full potential in theming web parts to make sure they play nicely in every environment.
After this session, you learn all you need to know about web part development and branding web parts.