Interesting thoughts mate. I would ask why...did the colour green and red fall into the categories as explained...what was the motive behind it. Colours are then just visual indicators? for instance the wiki gubar linked...has hot and cold taps..blue and red..I assume in this particular case...blue was adopted for..the human perception of cold..(not green for go)...and red was our perception of heat?? This would be an interesting point from a blind persons perspective....as they have not actually had the pleasure through unfortunate circumstance to see colour. I will also ask...was the 'green' for go button and 'red' for stop button on machinery (like a press) allocated before the invention of traffic signals? if so, why? I think you are right though...in the end colour is meaningless and it comes down to a learned system? like taps...the left is cold, the right is hot..LOL unless your Dad plumbed the joint...interesting stuff.

It would be interesting to see in times gone past (pre industrial) what colours were used to represent things..and whether we have simply adopted them or created new ones.

Cheers bullet