Well Standby_Selection_Back is for selections in areas which do not have Focus. if you have Focus in the Sample Editor then changing this should not affect it! It should affect the colour of the selection if you put Focus on a different area.
So, from your description, I think it is working correctly.
It’s the same for what you have selected in the Disk Op, which is the current Instrument etc etc. All these will be that colour if not in Focus to show they are the current. You are welcome to set the colours the same for in Focus and not if you desire.
I assume this is what is indicated by “Standby” in the name of the property. So set both Selection_Back and Standby_Selection_Back to the same value/colour if you don’t want to distinguish between selection in the focused area and not.