What's the difference between Red/Black deployment and Blue/Green Deployment?

I've heard both used to describe the idea of deploying an update on new machines while keeping old machines active, ready to rollback if an issue occurs. I've also heard it used to describe sharing load between updated services and old service, again for the purpose of a rollbacks --somtimes terminating inactive older patches and sometimes not.

My understanding also is that it is strictly for cloud services.

Can someone help to demystify these terms?

[META]: I apologize if this is not the correct site to be asking, I didn't think server fault or superuser were appropriate.