The colors should use some of the blues, greens and maybe burnt oranges. The final winner will need to give us five images:

1) The logo
2) Flat image similar to the Custom Logos below (https://www.lightningdesignsystem.com/icons/)
3) A 60x60 version for an icon in the AppExchange.com
4) A 280x205 version for a tile in the AppExchange.com
5) a 1200x300 version for the banner in the AppExchange.com

Examples of the icon, tile and banner can be shown by going to the AppExchange.com and searching for "Simple Signature" and "List Browse". You will see a tile come up, and then if you click on the tile, you will see the big banner.

List Browse
https://appexchange.salesforce.com/listingDetail?listingId=a0N3000000B3fiZEAR