There seemed to be a bizarre psychological experiment in play on my train home from central London last night. One of the two pairs of doors were out of order, and were denoted as such by four roughly 15-centimeter diameter blue circular stickers, two on each of the door windows, with an “!” and the words “Out of Order” printed underneath. On the outside of the carriage there were two further stickers, one on each of the buttons passengers press to open the doors.
At every station people stood at the doors, often staring “through” the stickers in front of their noses, repeatedly pressing the door buttons until eventually it was clear that they weren’t opening, before making a hasty shuffle through the carriage to the working doors at the other end. I even saw some folk standing outside of the carriage repeatedly pressing the stickers placed over the open buttons.
What was going on? Was that particular train bound for Shepperton filled with particularly dim passengers?
My hunch is no – but that the colour blue on a sign is one that we don’t associate with instructions – more that they are there for information, things like “Mind the Gap” – and so they just weren’t being seen by the people on or trying to board the train. A fascinating insight into user experience design and the way in which we take cues from the presentation of the information as much as we do (if not more) from the information itself.
mmitII 
Other possible reasons are a) people are resistant to change and will attempt to do what they always do unless forced b) people are not observant and again unless an instruction “jumps out” they will not alter their behaviour (to your point about colours) c) a combination of all of these. These are generalisations however those passengers who continued to press the buttons clearly demonstrated one or all of these behaviours.
Of course then there is option d) which is that people are just used to things on SWTrains not working until you hit them with a stick…