Cones provide colour vision while rods cells do not produce colour vision. Rods provide the vision in the dull light (darkness or night), whereas cones are known to give the vision during the day or bright light; Rod cells are more sensitive to light than cone cells and both do have visual pigments with the rod cells possessing rhodopsin and the cone cells having photo-opsins.
The brown spotted deer would spread their genes more than the white spotted ones which would eventually lead to them completely overpowering genetically the white deer in future generations.
