I read this idea mentioned in an old thread and wanted to see if it was still on your radar. I think this would be a fantastic improvement to the color toolbar for quick color selection and hope to see it in the program!
I imagine it as three vertical sliders for hue, saturation, and value, stacked vertically in the toolbar. I created a mock-up image with the HSB Color Toolbar to make sure the idea is clear.
Thanks for considering this feature!