t 'n t luoma

Don't take this as an authorative answer, but if I recall this right: Blue LEDs are far more expensive to produce, and their asking price used to be as much as 50x that of red or green.

As for dual-state LEDs: I don't ever recall seeing them in any combination involving blue.

Arve's right about the LEds, but that doesn't answer why those colors have been used for decades before LEDs were even thought of, does it? :-)

Blue has always been an expensive colour, especially if you want it transparent. To make good blue glass, you need cobalt. One thing is that cobalt minerals are rare, another problem is that up to last century the refining was terribly expensive. The best cobalt smalt was more expensive than gold. Green, on the other hand, comes from iron. Cheap bottle glass is naturally green, making clear glass is more difficult (demands purer ingredients). Good ruby-red glass contains traces of gold, but not very much, and you can make OK red glass without too much expense.

I have the same problem and I'm looking in the net for an color filter to put on the red led or on the green led to avoid this problem.

Do you think it is a good solution?

{{mmiki: I think a good solution is any one that works. The problem is that often the device has one light which turns either red or green, so it is difficult to figure out the status unless the device itself is changed -- TjL}}

well for electronics, most use LEDs, which generate light based on the emitted frequency between two types of metal. GaAs has been the cheapest and most common for a long time, and it is capable of red/green/yellow frequencies. blue and white are much newer and more expensive, blue being an especially small wavelength to achieve.

to tell you the truth, i'm sure companies have thought of the red/green problem, but I think since it's been the common option in the industry for so long, that's just the way electronics designers choose to save money/meet simple expectations.

I guess it has something to do with the way the human eye/mind perceives these colors...
Green is a warm, soothing color, almost serene (depending on intensity and other factors) and probably that's why (or because of!) nature is full of green shades. Red on the other hand, is alarming, it's less appealling to the eyes, and therefore more often used as signs for warning or alerting.

Something like that...
... I think... :-)

I did some research on this for Section 508 and color in general. Here's a useful link: http://www.du.edu/~jcalvert/railway/cnwdist.htm

Basically, red is visible at long distances, which helps with train signaling. Green isn't so much, and you need to know to stop more than you need to know to go.