Does anyone know how to change the color of the right click menu in SSMS 2016 with the dark theme enabled?
The Dark Theme is still under active development and the work-around to enable it should be used for testing only. If you are testing it, then check Microsoft Connect for the issues you find, if they have not been raised feel free to raise the issue yourself. You should expect problems with it until Microsoft enable it by default and as such I would recommend not using it until that point.
Here's how you can get the SSMS Theme for the editor. It's like a Monokai setup for SSMS.