How do I operate the device in the tetrahedron?

First of all, turn it on with the red button.

Now, play with the sliders.

When you move the three sliders on the left, the colors on one of the
monitors change.  The slider on the right selects which monitor is active.

In particular, each slider controls one color channel.  The left sets the
amount of red; the middle, the amount of green; and the right, the amount of
blue.

You want to set each monitor to the same color as is displayed just above the
monitor.