It's hard to tell if the next stage engine has been staged or not

[CiberX15]

After triggering a decoupler stage, the next engine stage drops into the first slot, and shows its fuel gauge. It’s impossible at this point to tell whether the engine has been staged and is active, or if it’s inactive. Which then leads to the nail biting question, “if I stage now will I activate the engine? Or drop the next decoupler?”

Optimally I'd like for the stage to not expand into the current slot until it has actually been staged. Additionally color coding stages to indicate whether they are active or not would also help.

[The Aziz]

I like to have my staging extended all time (KSP1 -like) so definitely some better indication is needed.