This little app is so useful, I use it every day. Awesome work!
One little bug I've found: When using multiple monitors, I've noticed that the source of the eyedropper window can sometimes be really "off" (the area its picking color from does not match where the mouse is).
I haven't figured out exactly what causes this, as I've noticed it isn't always consistent. My guess is that it might have something to do with my monitors being different resolutions (1600x900 and 1920x1080), or it could also be the DPI scaling is different on each monitor (one is 100%, second monitor is 150%). Because if I unplug my second monitor and only use the main display, I don't notice any issues with Eyedropper then.
Either way, I've been able to get around the bug by moving whatever window I want to pick colors from to the "main" monitor, or just restarting Eyedropper.exe a couple times.
It's not a huge issue, but just wanted to make you aware of it.
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Pro Tip to anyone else downloading this app: You can use AutoHotKey to set Eyedropper to start from a hotkey shortcut. I use [Windows Key] + [N] to launch Eyedropper. It's super useful!