One nipple darker than the other. Normal?? Caused by BC? TMI PICS

Hey guys,

I had a pregnancy scare recently and started paying more attention to my body. I noticed one of my nipples is darker/more purple than the other one is? My areola's are practically the same color and those haven't darkened at all, it's just the nipples.

I just had Nexplanon inserted not too long ago, so I'm not sure if that could be a cause of them darkening. Is it normal? I'm 19.

Left

Right