Whenever a system is inoperative, pilots or mechanics apply a so-called ‘INOP sticker’ to the associated controls (switch or pushbutton) as a reminder not to operate the system. unfortunately, the stickers are often coloured red which renders them very conspicuous during the day and under good lighting conditions, but rather difficult to read at night – although it seems that red is one of the best colours to see under low-illumination.
Not long ago, after a night landing as PM (Pilot Monitoring) I attempted to start the APU although as a crew we both knew (and briefed) that it was inoperative. I didn’t notice the red label which was applied to the controls because the flight deck was (intentionally) dark not to ruin our night vision. Luckily I quickly realised my slip and reset the controls (shut it off).
Maybe we should consider using a (temporary/removable) sticker that actually prevents using the switch/pushbutton or – as often already done – de-activate the system completely so no action can activate it.