When we do the experiment that chlorophyll is necessary for plants then we take veriegated leaf to perform. At the end of experiment we obsereve that only green part turns blue black in colour not the white part. Why is it so, though the starch must have transported to white part also.

Total absence of plastid pigments causes certain parts of the variegated leaf to have white patches.  In these plants only the green parts of the leaf can photosynthesize. The zones where chloroplasts are not present are zones where no photosynthesis will occur. Since no photosynthesis occurs here, no starch is to be found here. Starch cannot get transported here.