Thanks Shawn. Your photo also reveals some of the nature of the plasma in the photosphere. There is no solid surface as it appears in the photo. What you are seeing is called optical density. How far you can see into a gas before it becomes opaque. Think looking into a thick fog. If you look at a perpendicular angle (coming out of the center of the photo toward the viewer) you see through the least thickness of plasma. That is why it looks white as you can see deeper into the gas. As you approach the limb the image gets darker. This is due to the increasing thickness you must look though at an angle greater than perpendicular. This is called limb darkening. The sunspot is dark due to the slower velocity of charged particles below where you see the spot. Intense magnetic fields alter the trajectory and velocity of the charged particles in the intense field. Remember temperature is not the same as heat. Temperature is particle motion. Thus the darker spot results because of inhibited motion resulting in lower temperature...............thus the dark spot. More exactly, inhibited convective up welling below the spot.  Attached is a picture of electrons going in a circle as a result of moving in a magnetic field. Same mechanism.