So they see in shades of grey, just like a black and white television. Butterflies have compound eyes like many other insects. They see better than humans in ultraviolet range upto 300 nm. They require this ability to spot the central nectar bearing part of the flower. This helps the plant in pollination.
Insects have compound eyes.
Each eye has many shiny lenses, which cast a small image. These multiple images are integrated by their 'brain' and the object is seen. Unlike our lens , these lenses cannot focus. Compound eyes are advantageous to insects since they provide a better field of vision, so enemy or prey can be seen in all directions. The hawk has the sharpest eye.