I just used it for the first time a week or so ago to make some aged pu erh. After just five or six infusions, it's quickly taking on a blackish coloration in some areas. This seems strange to me. Of course, the ability to develop patina is one of the attractions of clay teapots. However, I have several others, Chinese and Japanese, and none have ever changed color this dramatically this quickly. Note the discolored areas, which cannot be washed off:



To add to the weirdness, the inside does not seem to have changed color at all:

Unfortunately, I neglected to take any "before" pictures, but basically it was just a uniform reddish orange.
Any thoughts? I have no idea what kind of clay this pot is made from; I don't know if it is perhaps more porous and just absorbing the tea more quickly than my other pots, or if this is something to be concerned about. The fact that the inside still looks brand new seems particularly strange to me.
Thanks!