If you go into the Nvidia GeForce Experience application, you can use the LED Visualizer to decrease the brightness to zero (effectively turned off). That's how I have mine set. Sometimes you need to repeat after PC reboots.
EDIT: Checking the visualizer reveals that there is actually an option to turn LED effects off altogether.
The dragon and MSI logos on the side just above the pair of SLI connectors are backlit by white LEDs. There is no way to disable this other than by unscrewing the cooler and disconnecting the cable.
If you go into the Nvidia GeForce Experience application, you can use the LED Visualizer to decrease the brightness to zero (effectively turned off). That's how I have mine set. Sometimes you need to repeat after PC reboots.
EDIT: Checking the visualizer reveals that there is actually an option to turn LED effects off altogether.