Hello there, thanks for writing in. Please be reassured that it is very much normal to find color, size, position differences in both breasts. Breasts tend to differ from each other in these aspects as they respond differently to hormonal influences at the time of puberty. Having said that, I would like to emphasise about breast self examination regularly and the warning signs if abnormality like nipple retraction and discharge ( bloody, serous, greenish) lump in the breast, puckered skin over breast. However, as your mammogram is normal, there is nothing to worry about and it is quite reassuring. I hope your concern is addressed satisfactorily. Take care!