Between the value 400 nm and 700 nm there is an infinite amount of real values that can represent the length of a wavelength.
If we consider that each differente wavelength represents a different color, therefore there are infinite possible colors in the interval from 400 nm to 700 nm.
But if we consider only certain intervals of wavelength as certain colors, we can have for example 7 colors:
Violet, Indigo, Blue, Green, Yellow, Orange, Red.
