Mac OS X 10.11.6
Mac Book Pro
When using the color picker loupe to select a colour from the screen the color selected when you click the mouse is not the color beneath the mouse pointer.
The larger view window is accurate but the smaller swatch window displays the wrong color. The color displayed in the swatch window is used on the mouse click.
Use the digital color meter found in Utilities to obtain the correct code and paste that into the color picker.