FactionPaint is a Torch plugin for Space Engineers. It allows players to paint blocks that are owned by their faction members, themselves, or nobody.
Once you have Torch set up, just drop the FactionPaint.zip file into your Plugins folder.
Install Visual Studio Community Edition (I used VS 2015), open the solution, and build.
Note: You may need to re-include the references, as they utilize hard-coded paths.
Torch has a wiki page on setting up the references and other plugin development information here: Torch Plugin Development
I mostly wrote this for my buddy's server, releasing because I've seen the same question come up before. The code is super simple, so you can customize it as you need.