How to test led with digital multimeter?

The user set up the multimeter to diode gears. then measuring the good from the bad. the red test pen should be connected to the positive led, and the black one to the negative led. if lit the led is good. Contrary, The led is broken, it can’t be used.
Meanwhile, The screen will be display that led of forward voltage drop(unit as mV).
Red led of forward voltage drop around1.8V
Yellow led of forward voltage drop around2V
Green led of forward voltage drop around2.2V
Blue & white forward voltage drop around3V