Flag power plants as emergeny provider

Just like I can flag a power plant as a surplus provider, I'd like to be able to flag it as an emergency provider. Emergency power should be visualized by a different color in the main power capacity indicator clearly showing me how much regular power I have and how much reserve is there on top of that.
Usually I'd configure my diesel engines as emergency as I never want them to actually run.
This is just about visualization. Making sure that only emergency equipment is running when I'm on emergency power can easily be achieved through priorities.
Right now my indicator shows 12 MW of capacity, but 6 of them are diesel and I always have to gauge where half consumption is.