tickled pink

be tickled pink
be tickled to death
(very happy, delighted)

Example 1: She was tickled pink when Dave finally proposed.
Example 2: I was tickled pink when I got his autograph.
Example 3: His parents were tickled to death when he decided to marry her.

-----------
I think that this likely comes from the fact that when a person is excited, his/her face might become a little rosy, but it could also originate from the game "pink belly" in America where children push another child to the ground and tickle the kid's bare belly until it turns pink.