@leocg Thank you for your reply. I did find an associated flag in opera://flags/#color-picker-eye-dropper, but it doesn't seem to work. Also, I saw that it was possible to have a color picker when I click on a color (if none is present, I create a rule) in the Style tab of the Element inspector .
It's not as "User friendly" as having it directly in the Element Inspector, but it gets the job done.