Make the colour picker give you a live preview of the clicked colour without having to click 'ok' every time (like on Photoshop).
Currently, if I'm changing the colour of a circle (for example), I have to choose a colour on the picker tool then press 'ok' to see how it looks and go back into the colour picker to keep changing it slightly. If you could see a live preview of how the colour would look in the background against all the other elements, this would save so much time!
This tool is currently available in Photoshop but not Illustrator.
Again, this should be already implemented - not just via a swatch panel - the colour picker!