Hubble’s main function is to measure the brightness of light reflecting off objects in space. It’s easiest to measure that in images captured in black and white. Scientists use broadband filters to separate the brightness of the light into long, medium, and short wavelengths. These wavelengths are then assigned a color based on the visible light spectrum. When the three images are combined they create a true color image— essentially what an object would look like to the human eye (if we could see as sharply as the Hubble).