The sentence can be completed as follows:
"The wavelength range of colors visible to humans ranges from 350 nm to 750 nm. light that most of us perceive as red is at 750 nm."
In fact, each different color is associated to a different sub-range of this range of wavelengths. Approximately, they are:
- violet: 350-450 nm
- blue: 450-495 nm
- green: 495-570 nm
- yellow: 570-590 nm
- orange: 590-620 nm
- red: 620-750 nm
