Exceljet

Quick, clean, and to the point

Select column differences

Windows shortcut 
CtrlShift|
Mac shortcut 
|

This shortcut will select all cells that don't match the value in the active cell in a column, or selection within a column. Note that this shortcut depends on the location of the active cell in a selection. You may want to start your selection with the active cell or move the active cell after the selection is made.