Why do you see color when you put a plastic transparent ruler on your eyes?

Because this kind of ordinary light is composed of seven colors (red, orange, yellow, green, blue and purple), if you put it on your eyes with a transparent ruler, the light will be refracted, and the refractive index of different colors will be different, so that each color of light will be refracted and separated, and you can see colored light. There are many such examples in life, such as rainbows in the sky after rain, reflections in mirrors in water and so on.