It’s alright to tint the accent colour slightly, that’s fine. However, while the proposed UX is much better, it still doesn’t offer something on par with other operating systems/desktop environments.
Having one drop-down with pre-defined colours will work for most users. A “Custom colors” entry drop-down menu entry would open a window, and give a clean UI. I don’t mean no disrespect to all the previous authors of this dialogue, but it is ugly, with the modifications, it looks even more bare and unpolished.
Also I don’t think we have the text selection and menu focus background configurable currently, do we?