All school children learn: Go with green. Stop at red. Green is good. Red is bad. Stick to this and you’re less likely to be run over. Traffic lights are simple. Prices are not. For some it’s good if soybeans and wheat, coffee beans and cattle, stocks and money become more expensive. Others prefer it if things get cheaper.
Source: Wall Street Journal, 2010-09-27, page 26.
The Wall Street Journal used to see it that way, too. For resources, indices, and stocks, the price went down in dark gray and up in light gray. It was easy to differentiate and read. You could form an opinion on your own. Now resources and indices are green if they become more expensive. And red if they become cheaper.
Dear schoolchildren, sadly the adult world is more difficult than traffic lights. Look left and right before you cross the street. Even if the traffic lights are green. Dear chart designers, use more gray.