It uses a camera and some software to simulate 3 different kinds of colourblindness.
Red green - by averaging the red and green channels to give a yellow channel (there are two subtley different forms from loosing the red or the green cone in the eye, but the actual sensitivity of the red and green cones are very similar)
Blue yellow - by loosing the blue cones
If you rub a very rough surface with one hand and a very smooth one with the other then an intermediate surface will feel rough to one hand and smooth to the other. Very simple but effective.