Ctrl+click the swatch to mix it with the current color
There is a small thing in Corel Draw, that AI could benefit of too.
If you have an object selected and click in a different swatch with a Ctrl held, it adds a bit of clicked color to your current one, blending them.
Like if you have a yellow CMYK 0-0-100-0 and Ctrl+click in 0-100-0-0 magenta swatch, you will have 0-10-90-0, 0-19-81-0, 0-27-73-0, getting more like the clicked swatch with each click. Same in EGB Very convenient for adding color reflexes and picking a color in general.