It's not essential but you'd be surprised at how bothered buyers can be by paint colors. Depending on how loud or bright they are, they can distract buyers from being able to see the bones of your house.
The condition of your paint matters too. We painted right when we moved in to our house 8 years ago. Life and small children have definitely left their marks on our walls. We're having the house painted when we move out if for nothing else, to make it look fresh and clean.