Why do my nipples appear darker?

I am on the birth control pill and I take it everyday within the hour and I have never missed one. I have been on it for 2 years. My boyfriend and I always pull out too.

I’ve recently started noticing that around the 2-3 week of my pack my boobs get really really sore, but then it fades away during week 3-4.

Anyways this month my boobs were very sore and for only 1 day I had stinging nipples. There is no more stinging and the tenderness is slowly fading. Although my aereolas appear a little darker.

I absolutely do not want to be pregnant. Do you think this could just be my hormonal birth control???

Also I never get my period on my birth control (doctor is not concerned) and I have no other symptoms. The darkness of my aereolas seems to be lightening but it is hard to tell since I just noticed the darkness yesterday.