What is the colour of light related to?

Visible light makes up a part of the electromagnetic spectrum, a continuous range of wavelengths which we use to order different types of radiation. Visible light spans from 400 nm to 700 nm and mostly appears as white light. However, white light can be split by a prism into its separate colours, these being the colours of the rainbow as each colour has its own wavelength range within that of white (visible) light. Blue, for example, is at the 400 nm end. When something we see has a specific colour it's because that object absorbs all the colours of light expect the one we see. That wavelength (and hence colour) gets reflected back to our eyes and so our brains register it as being the colour that goes with that wavelength.

Basically, the colour of light is related to wavelength.

Light is electromagnetic wave with wavelengths between 400 nm to 700 nm. The wavelength of this electromagnetic wave defines the color we perceive through our eyes.

White light is made up of a spectrum of wavelengths of light varying in colour