Never been a big fan of "Yes It Is" myself. The harmonies sound slightly out of tune to me - I think it might be George's vocal which is out.
Been giving this a few more listens and I'm now wondering if it is Paul's vocal which goes out.
For example, on the line "Please don't wear red tonight" I think
Paul goes from singing the high note, above John's main vocal, to singing a low note at the bottom of three harmonies when it gets to the word "tonight".
If it is Paul then I suppose he can be forgiven (
). It's a big leap vocally from the high note to the low one and it must be very hard to pitch that perfectly, even for as good a singer as him.
Does anyone have a transcription of who sings what?