People who are color blind most likely have deficiencies in their

Cone cells.

Explanation:

Eyes are important sense organs of the body that  enables us to see the different objects. Eyes also plays an important role in sensing the inside and outside stimuli.

Two main types of cell present in eyes are rod cells and cone cells. Rod cells are involved in the intensity of the light where as the cone cell enable us to see the different colors. The color blind people have deficiency is their cone cell as these cells helps in identify the color.

Thus, the answer is cone cells.