Pocket CVI is on its way to your Downloads folder. If nothing happens, start it manually.
Double-click PocketCVI.dmg in your Downloads folder. A window opens with the app and a shortcut to Applications.
Drop Pocket CVI onto the Applications folder in that window. You can then eject the disk image and delete the .dmg.
Open it from Applications, then press ⌃⌘⇧P and click any pixel on screen. The color is yours — and on your clipboard.