Modern screens use combinations of pixels emitting in red, green, or blue at various intensities to create the images and colors we see on the device. With the understanding that RBG creates white light, using "pure" R,G, or B light (and combinations of RGB intensities) as an illumination source of an object demonstrates what our perception of color means in regards to light reflection and aborption. 

RGB Illumination

The image above demonstrates an object (a crystal latice model) illuminated by white and "pure" R, G, and B light. You can also tune the hue in 5 degree increments, so a touch of red can be added to green to change the "color" of the object rather dramatically, as demonstrated in the image below. 

RGB Illumination Example