S2721HN, flashing colors

We just upgraded monitors for the entire office with Dell S2721HN Monitors (24 of them). Every single monitor flashes colors any time the monitor doesn't have an input. When Windows turns the screen off after 1 minute (default time) every monitor starts flashing. Before logging in after a restart, the monitors are flashing. Shut down the computer, monitors are flashing. It looks like there is a rave here every morning!

I went through the monitor settings and cannot figure out how to make it stop. Every previous monitor we had just went dark when in standby. Any suggestions on how to turn this off?