The Gmail M-velope has been updated slightly...

Old:
https://mail.google.com/mail/images/2/5/logo3.png

New:
https://mail.google.com/mail/images/2/5/logo4.png

Good catch!

Gmail WebApp in Chrome also has the same icon.

https://lh5.googleusercontent.com/_8ghhA1BQqIM/TNqr_ZHBlVI/AAAAAAAAWnE/7XpbNl3k2KA/Screenshot.png

really slight... 0_o

Update from the Official Gmail Blog:

<< If you visited the Gmail log-in page recently, you may have noticed that things looked a wee bit different. We decided to give this page a bit of a facelift and updated a few of Gmail’s other pages while we were at it. Our goal was to keep a familiar look while freshening up the graphics and trimming down the text (we cut out over 250 words in the process)...

We also updated the Gmail logo, brightening the colors and making it more in line with the latest Google logo... >>

http://4.bp.blogspot.com/_JE4qNpFW6Yk/TNs3YeLt6JI/AAAAAAAAAwA/Vatl3XA9e94/s600/logo_before_after.png

http://gmailblog.blogspot.com/2010/11/gmail-homepage-makeover.html