The internet giant will soon provide its users with a new Custom Themes section that will have two new options: Light, Dark. With this, you can make whatever changes you want to your own theme on Gmail.
Not only this, you can even select images directly from, Google+ or even use a simple image URL which is recognized automatically by Gmail and appears as your new, customized theme.
Additional options that will allow you to browse through Google's “searchable featured photos section” and select the photo/image that you think will fit in as your new Gmail theme. Plus, Google also allows searching for images on its “featured” tab as well.
This means that you can set various photos/images as your Gmail theme and can even bring back the fond memories you had or are associated with that particular photo/image.
So check out Gmail in the next couple of days for new options.