Neither the “on” nor the “off” state has an icon which you know immediately and without a doubt to mean “on” or “off” without any further context. If you see this you don’t know what it means, and if you see this you don’t know what that means or does either, nor do you know what means (is it on or off or standby?), until you get context. One gets context by seeing the icon painted on a switch or button, and by seeing the icon change shape or color when it’s used. For this reason I see fiddling with the RT power icon as bike-shedding and a waste of time - one gets the required context by trying it and by reading this page which every user without exception should read else they’re gonna have a bad time: http://rawpedia.rawtherapee.com/Getting_Started
The one unambiguous solution, if someone wanted to spend their time doing it, is to replace the power icons with the words “On”, “Off”, and “Inconsistent”, but the last word is way too long for its purpose, and the translations of “on” and “off” can also be unusably long in some languages - “włączone, wyłączone, niespójne” in Polish, “encendido, apagado, inconsistente” in Spanish, etc.