Simple Colour scheme add-on for themes

Issue: The current colour picker in the new themes let's us choose one base colour and it auto-assigns the primary, secondary and accent colours based on the selection. While it works great and is really minimal, it does feel too restrictive. I've even seen people talk indirectly about this in the forum and community, like selecting the clock colour, etc etc. Like for example, I wanted to keep this slate grey theme, but with red accents since I have a OnePlus device. But I have no way to change that currently, and I'm stuck with the pastel violet.

Solution: While obviously letting the user select the whole colour spectrum wouldn't be a sensible solution, but a small (optional) button below the preset options would be nice. If clicked, the menu would enlarge a bit and a new row would be added at the bottom. There users can select the primary, secondary and accent colours, and the system would fill the rest of the shades by itself as usual. Just 3, not more not less.

Would be a great add-on I think. What do you think?