Why does the intensity of the blue solution color lessen as the reaction proceeds?

Why does the intensity of the blue solution color lessen as the reaction proceeds? 

Question 4 options:  The blue color of Zn2+(aq) lessens as it is reduced  to Zn(s).  The blue color of Cu2+(aq) lessens as it is reduced to Cu(s).  The blue color of Zn(s) lessens as it is reduced to Zn(s).  The blue color of Cu(s) lessens as it is reduced to Cu2+(aq).