Anything we see around us that have colours are not actually colours but photons travels with different frequencies and our eyes detect that frequencies in form of colours.
How photons travels with different frequencies-
Electrons are revolve around the nucleus in different shells in an atom.
Every particular electron revolve in an particular shell. When photon collide with electrons, the electron absorb the energy of photon.
By absorbing the photon energy, the electron goes to the next energy shell for a short time of period (10^-8 sec)
The electron goes to the next energy shell called excited state.
After 10^-8 sec in excited state, the electron come back to it’s original energy shell called ground state.
When electron come back to ground state, it release the energy of photon which is absorbed by it. It release photon in a particular frequency range. And the whole process is continuous.
The released photon strike on our eyes. The light receptors in eyes can transmit the message to brain and brain can detect the this in form of colour and make an image of that object so that we can see an object which has colour.
There are more than 10 million colour detected.
Black and white are not colour because black is form when all the light Ray’s or all the photons can be absorbed and white is formed when all the light Ray’s are reflected from the surface.
Anything which is transparent can pass all the light Ray’s through it and would be invisible if 100% light rays can pass through it which strike on it.
The range of visible light is 380 – 700nanometer(nm).
And all the colours we can see have in the range of visible light.