The color of the light is determined by its wavelength.
The color of objects we see is actually the wavelength of the light that it reflects towards our eyes and this wavelength is determined by the energy of light absorbed and emitted by that object.
The color of green leaves appears to be green because it absorbs the light and re-emit the photons having a wavelength of green color (520-565 nm).
Different colors have different wavelengths. For example, Red color has the longest wavelength (625-740 nm) while the violet color has the shortest wavelength (380-430 nm).
