If you’re thinking of creating some Ubuntu MATE artwork then to following images might be of use.
Ubuntu MATE Logos
The following Bazaar repository contains all the Ubuntu MATE logos.
Yuyo will be the default theme for Ubuntu MATE starting from the 15.04 release. If you want to contribute to Yuyo development then you can find it hosted on GitHub.
Please feel free to submit pull requests that address any of the outstanding issues.