Another thing to check for with sticky headers is how it behaves when the page is zoomed. Often, the header increased in size proportionately, which can shrink down the effective reading area quite a bit. Add in the frequent sticky chat button at the bottom, and users may be left with not a lot of screen to read text in.

There can be a logic to keeping the header at the top like a menu bar, and I applaud you if you take an approach that focuses on value to the user. Though I'd still say most sites that use this approach, don't have a strong need for it, nor do they consider smaller viewports except for portrait mobile.

Configuration is great, though it quickly runs into discoverability issues. However it is the only way to solve some things - like you pointed out with colors. I know people who rely on high contrast colors and others that reduce contrast as much as they effectively can.