Paul wrote this one (yes, Lennon/McCartney officially) and gave it to Ringo to sing. Ringo did a fine job with it, since it did not require much of a range. Donovan helped McCartney with the lyrics "sky of blue, sea of green" Paul has continued to popularize this song/film throughout the years. Song was a hit on both sides of the Atlantic, hitting no. 2 in the U.S. Personally, I think the entire film rocks.
"There's nothing more to be read into it than there is in the lyrics of
any children's song." ~Paul McCartney on Yellow Submarine