I couldn't get a closer photo with my camera. She's regularly in my garden and behaves like a blackbird
It is a male, and the yellow, if it stays with the bird, is something stuck on or attached. It isn’t part of the tail.
Have tried to enlarge your pic ... looks like some sort of, maybe plastic, plant label?
2013 photos & vids here
eff37 on Flickr
I'll keep feeding him and hope it drops off of it's a tag of some sort. Poor wee bird!
Do let us know if he returns
He comes every day :-)
Hope whatever it is, drops off and causes him no harm.
A word of caution, you may want to change your user name from personal email, this is an open site and you could end up with unwanted mail and hassle. Go to the top right little symbol, click profile, down the right you will see, edit profile, you can now change details at the top left, save profile when done.
Beauty is in the eye of the beholder.