Finally lots of changes are seen in Gmail including Voice video chat,canned response,IMAP,Emoticons and another recently added feature is Gmail themes which is available now! If you log in to Gmail account you will find the default skin is changed to a new bluish (Beautiful) skin.As of now,there are several theme background which can be accessed from the Theme Tab in Gmail Setting.
To change Gmail skin head over to themes tab and select your theme which will be applied instantly.Some of the themes are quite bright/dark (especially Terminal theme) whereas themes like Desk and Classic will give your mailbox a fresh look!
To completely change the Gmail theme you can also use Gmail better skin addon built for Firefox.

I want that pink theme in the 1st row but it doesn’t appear in my Theme Tab.
Sad. =(
i’ve been reading about this all over the blogosphere… i don’t think it was such a big and essential addition… anyways the only good thing is that this is an indication that they are constantly working on it…