Why does my blizzard leopard gecko have 1 spot on her tail?

I have a blizzard leopard gecko...she is about 3 years old and has no pattern besides gray/silver on top and white underside but in the recent months i noticed a small black spot on her tail that hasn't gone away with shedding. If anyone knows what it may be and if i should take her to the vet or not please let me know.|||Hmm.. a black dot on the tail? could it be decaying skin? Its hard to say without a pic but at 3 years her color change should have been done. So if i were you id bring her in coz ive never heard of a adult that age randomly getting spots. Itd ease your mind for sure.