Mule deer

Mule deer can have a mostly white tail, but the tail at least has a black tip. "[Mule deer] have a narrow tail with a black tip and, unlike the other common species of BC deer, the Whitetail, the mule deer do not carry their tail upright when running." http://janamalinekphoto.blogspot.com/2013/02/the-deer-family-of-british-columbia.html

If it has a white tail, isnt it a white tail deer? If i remember correctly, mule deers dont have white tails.