What part of a light determines the color?

Answer 1

The wavelength. That means how far apart the waves are spaced.

Light is electromagnetic energy just like any radio signal. The main difference is that

if your favorite FM station is at, say, 98.3 on the dial, then visible light would 'tune in' anywhere between roughly 3,600,000,000 and 5,400,000,000 on the same dial.

We can't build a radio that can tune to this range, but your eye is very sensitive to

those signals. The color you see is determined by the exact number in this range ...

red at the low end, violet at the high end. If the radiation is outside this range, then

your eye no longer responds to it. These numbers refer to the 'frequency' of the signal, but the signal can also be described by its 'wavelength'. That FM station at 98.3 on the

dial has a wavelength of about 10 feet, whereas the longest visible wavelength ... red light ... is about 0.00003 inch.