Color Theme sharing

i understand that these are saved somewhere within the project.
is there a way to share these between artists?

I was looking for it also. This answer has the solution.

The file [ProjectName]/Saved/Config/Windows/EditorPerProjectUserSettings.ini stores this information as well as folders colors, tabs placement, UMG preview sizes and a lot of other stuff. Open it up and you can sniff around to find out more =)