I got 2 application suggestions for Mac:
They are OS wide color pickers so they can be used to pick colors from anything you see in your screen without having to feed it an image or take a screenshot first or something.
I own both and I've used them quite a lot, but to me Color Snapper has one killer feature: A zoom toggle that zooms in really close when you hold down Ctrl. This is amazing because you can zero in on top of the area with lesser zoom super easily and then with one single modifier key zoom in close enough to differentiate pixels and the cursor will move slower too. Additionally, both of these applications have shortcuts for resizing and zooming the magnifying glass once it's activated, but they take more effort to use. I've tried to jump over to using SIP a few times, but I always end up missing the toggle zoom and go back to Color Snapper.
I do also like that with Color Snapper you pick the color and then it suggests the different output formats, whereas with Sip, you gotta choose the format first and then pick the color. It's not a big deal though... If you pick a color in the wrong format, you can change the format and copy the color to your clipboard again from the color history.
SIP has CMYK color output, and Color Snapper doesn't. They both have trials.