Is this a pressure sore?

I have a question about a Sacral area possible pressure sore on an elderly caucacian patient 60years old whom weights about 180lbs she came in with s/p hip fx. and on her assessment we found that she has a light yellowish color on the sacral area about 1.5 x 1cm... we had to spread her buttocks open so that we could see this... there is no depth to it and there is no drainage or anything... she is continent and is able to walk with assistance and a walker... We've been treating this with santyl for a week but its going nowhere... I think this is her normal skin but since its hidden because of her buttock folds she has a different lighter skin color on this area.... does this condition has a particular name or is it actually a pressure ulcer?... she doesn complain of any pain or discomfort.. and they were not treating this at the hospital (maybe they didnt see it since you had to spread open her buttocks....) we put her on a low air loss mattress but as I said I have the feeling that this may not be a P. ulcer... any thought on this