I'm working on an online trading platform and my client wants to change the buy and sell buttons to neutral color instead of red and green and I can see most of the platforms use red and green. Is there any scientific reasoning for this?
Green connotes ideas like “natural” and “environment,” and given its wide use in traffic lights, suggests the idea of “Go” or forward movement. Green was also in Performable's color scheme (along with black and gray), so a green button fit a bit more nicely into Buy criteria.
The color red, on the other hand, is often thought to communicate danger, blood, and warning. It is also used as the color for stopping at traffic lights. so a red button fit a bit more nicely into Sell criteria.
Numerous studies find that the color red is programmed into our minds as a cue for danger. This has traditionally been used by retailers to grab a customer's attention by painting their SALE signs red. Red and green are complimentary (opposite) colors, and it's only logical to use green for the opposite buy.
This article has more on this subject if you're interested.
In general, red is a color that a user categorize as a danger or something bad, where green is the opposite. The thing here, that the action expected from the user is not to choose between good/bad, it's requested to choose to buy/sell. those actions are not corresponding with the red and green colors.
As an Ex- product manager of a trading platform I can say that the red and green colors, in this trading industry, are more as a convention where nobody wants to break the chain since they can't anticipate/afraid of the outcome on the trading stats and volumes (users complain that the meaning was changed/don't know what to do/feel unsecured and move to some other trading platform)
Green belongs to the cold colors why red belongs to the warm colors. There is a natural understanding that these groups are opposed to each other. Moreover cold group is supposed to be brain relaxing while warm is supposed to be exciting (that's why hospitals are color schemes in blue and green). In terms of meaning I think the action of buying doesn't incur any immediate danger while selling does, reason for which the colors have been spread this way. But I think that here the important is the color groups, implicitly implying the separation of actions by belonging to opposite color groups. It would work to have blue and yellow for example.
There's a scientific reason NOT to have them red and green, which is that between 6%-8% of men are red-green colour blind and can't tell the difference so it's useless for them.
From the user POV using green and red either way round in a buy/sell choice doesn't seem to have any scientific basis. Both could cost you money if you made the wrong choice at the wrong time, so it's not like one is more 'dangerous' than the other to the user. This may well be why your client doesn't want them differentiated as such.
However, I've noticed in my trading platform of choice (a european one) that the buy button is green and a '+' sign whilst the sell button is red and a '-' button. Taking into account that, in nature at least, red is seen as 'danger', the cynical side of me says that's to give a subliminal nudge that selling and possibly taking your money and going is bad, but putting more money in for them to look after is good :-)
It'd be interesting to know if the rest of the trading platforms you surveyed have it the same way round or are swayed by the cultural/regional meanings Michael Lai pointed out depending on their target market