I'm not one to criticize Google for anything. I love what they do and any innovation is accepted with arms wide open. But Gmail themes just aren't hitting the spot.
We live in an increasingly visual-based society. That's why the concept of themes make sense for an e-mail account. Our e-mail is personal and we like to have our personality reflected through something we own.
But we also like consistency. This is where the importance of branding comes in. Gmail is a brand. We see the Gmail logo and we trust it. It's associated with security, speed, reliability.
Throw in a Gmail theme that totally ditches the Gmail brand we know and trust, and it just doesn't feel safe and comfortable anymore
If Gmail can find a way to make fun, clean themes that still connect with all the familiarities that I have grown comfortable with as a user, then they will have succeeded.
Granted, there are a few Gmail themes that do retain the Gmail logo. Still, with all their money and resources, could Google really not find better designers?
Themes that work for people are simple and bold, with a little flair of personality. Maybe Gmail should take a lesson from Twitter designers. Simple, clean, fun and I still get the Twitter logo I know and trust: