I think it makes sense to store important assets in GitHub, too. The hexagon images, including their raw photoshop form, are included in the project.
When I was more a graphic designer, and less of a programmer, I would store my files on an external hard drive. Now, I'm happy to share them. Please share the files if you use them. I've included screenshots that you can use to replicate the settings:
For Adobe Photoshop CS6: https://github.com/nbuechler/hex-psd-roles/tree/master/specs-for-replication
GPLv3