Named animals don't show their names.

I was playing Minecraft and I was trying to name my sheep jeb_ using a name tag and a anvil and it turned Rainbow but the name wasn't showing even when I got close to it. I tried naming other animals different names to see if it would work but it still wasn't working. And I tried going to other worlds to see if that would work but it still wasn't working. Can you please fix this? It would mean so much to me. Thank you,