Question

which part of our eye responds to wide range of colours (wavelength) and how ?

Answer 1

The Retina responds to the wide range of colours, or different wavelengths.

There are two types of cells in our eyes that perceive light – rods and cones. Rods are sensitive to low light intensity and cannot differentiate between different wavelengths of light.
Cones perceive greater details and are sensitive to different wavelengths of light (thus providing with colour vision). Each cone cell is most responsive to light of different wavelengths. Together, they distinguish between different parts of the visible light (spectrum) and perceive them as colour.