while i am going to calculate ESP with different basis set after optimization it will always become green surface. I am applying different mixed basis set but results becomes always same.
You have to draw a mapped surface. You can check the Gview Manual (Page 135): https://gaussian.com/wp-content/uploads/dl/gv6.pdf
and page 10 of this tutorial: http://chem.yu.edu.jo/rawash/chem%20495/Viewing%20Gaussian%20Structures%20with%20GaussView.pdf (from Prof. Rawashdeh's homepage http://chem.yu.edu.jo/rawash/index.html )