dark ring on vanity top

    Hi
6 months ago I had granite countertops installed in 2 bathrooms. Both were referred to as Barre granite and were from a quarry in Barre,Vt. They are muticolored black,grey and white (like a stone monument) They were sealed by the installer and recently resealed by me using an impregnator seal.
One bathroom is rarely used. I placed a ceramic soap dispenser with an unglazed bottom on the countertop and noticed that after it being left for about 2 months a dark wet ring appeared (the dispenser does not leak). I assumed that this was the result of water resulting from condensation (the bathroom gets a hot sun) I removed the dispenser and wiped up the water. However, after about 2 weeks the ring, although lighter, still remains. I don't know what to do at this point and would appreciate any advice.
Thanks,
Ralph