My areolas are getting darker. took a pregnancy test & its neg. what could be causing them to darken?

Lets review your que: Areola darkening is not an early sign of pregnancy. Darker signed people rend to have darker areolas. Changes in hormone levels can cause it. Early pregnancy usually has signs of fatigue nausea so if you have none of these symptoms it is most likely a normal phenomenon. If it is one sided then I would seek the help of a doctor