People around the world suffer from dark nipples specially after pregnancy, the reason is the excess of melanin in that area, it is due to hormonal changes. There is little one can do to prevent such hormonal changes. But you can try home made tips to reduce the color of that area, since these are natural products you will be using there is little or no harm in trying these. Remember first try this on a little area if you feel burning sensation use smaller amount.
So what you need to reduce the darkness of nipple is to try this mixture.
1. mix 1 tsp of milk powder, 1 tsp of honey, 1 tsp of lemon juice, and ½ tsp of almond oil; leave on skin for 10-15 minutes before wash off.
2. mix oatmeal with curd and tomato juice.. do as no.1.
Home remedies do take a bit of time to show results. Be patient, otherwise there are also safe skin lighteners in the market formulated for this purpose - papaya kojic acid soap, black licorice soap, dermaline skin whitening cream or lotion - and a high spf sunscreen..
These work well together to help you achieve the results that you want.