Is it normal to have the area of the removed mole a darkish brown/gray color the day after? (Photo)

The best course of action is to call the provider who removed the mole and get their feedback.  I can only speculate as to what happened but it appears that the mole was removed and that silver nitrite was used to stop any bleeding.  This can discolor the soft tissue a gray/brown.  It does not look like the wound was closed with sutures.  As always, you deserve the very best medical care so please see a Board Certified or Board Eligible Plastic Surgeon to evaluate if you may benefit from treatment. Good luck!
This content is for educational and informational purposes only. It is not a substitute for medical advice, diagnosis, or treatment provided by a qualified healthcare professional.  You should always seek the advice of your physician or healthcare professional for any questions you have about your own medical condition. 

The picture looks a bit atypical and there may be an infection there. Best to follow up with your dermatologist right away. The choice of using stitches is based on many factors which your dermatologist can capably decide on.