The case for mono- and duo-chrome designs
My former company had brand palette of four vibrant colors. In order for it not to become visually overwhelming everywhere, I set up a series of paired colors, with the idea that the colors would generally be used in pairs only, each time with a primary color + a highlight. It is possible to successfully take an established set of brand colors and minimize how and where the color is used.
Accessibility is definitely a good point I'm glad you mentioned it. I usually tell my students to use ColorBrewer or Coblis to find good color patterns for that. Do you have other tools you like to ensure that visualizations are accessible (especially when you get asked to add more color)?