Why is my hemorrhoid white?

Perianal mass. That would be an unusual color for a hemorrhoid. While hemorrhoids are a common diagnosis, there are other conditions which could be confused for a hemorrhoid such as an abscess. An evaluation by a general or colorectal surgeon would be recommended.
See a doctor. This needs to be evaluated. One possibility is that it is a lesion on top of the hemorrhoid and the hemorrhoid brought your attention to it.