What are the true complementary colors and their values ?
Being a webdesigner I learned that Green= 00FF00 Blue= 0000FF Red= FF0000 Yellow=FFFF00 Correct ?
And color theory says that Red is the complementary color of Green. Yet when I use http://kuler.adobe.com/ I get FF007F which is still far from Red. However when I use http://www.colorschemer.com/ I get true Red. For Yellow kuler gives me 7D00FF while colorshemer gives me 8800CC which are different enough for the naked eye to notice. For Blue kuler gives me FFD100 while colorshemer gives me FFBD00
A third tool colorschemedesigner.com give slightly different values (once adjusted to max saturation & brightness).
So as you can imagine, I'm confused as to what are the values of the complementary colors that aren't easy to guess with hex such as Orange and Violet and which color wheel is the most faithful.
I think you should be using RGB complements (in the "Light" answer). The RYB complements were from an era when people didn't know of light's primary colors being RGB. RGB complements look nicer, in my opinion. Here what some random dude named Lira had to say:
RYB is the traditional colour wheel, used by artists. Sir Isaac Newton was the first one to come up with this sort of thing. And it was kind of fun. Here, take a look:
Recognise it? It's the colour wheel Jason Beaird used in his "Color for Coders" article. Remember that, when we're in kindergarten and stuff, we're taught stuff like "Yellow plus Red equals Orange"? It all comes from this colour wheel, whose primary colours are red, yellow and blue (they're touching the darker triangle, poiting upwards). Warm colours occupy half of the space and cold colours the other half. That's like a colour Yin Yang. Almost too perfect to be true.
Indeed, it was too perfect to be true.
Scientists then find out that biologically, it doesn't really work that way. Anyway, after studying, researching, analysing, chopping and cooking colours, we ended up having the RGB colour model, ubiquitously present in stuff like computer monitors, TV's and so on.
As you might be assuming, the colour wheels are a bit different. The opposite of "red" in the RYB colour wheel is "green", whereas the opposite of "red" in the RGB colour wheel is cyan - you can test the latter by staring at something red (focus, try not to blink) and then looking at a white surfice: the afterimage is cyan. Here's an example:
That means you have two different colour wheels to choose your colours from. So, which one of them do you guys prefer?
A trivial definition of a complementary color regarding the RGB color space is as follows: given a color
(RR, GG, BB), the complement is
(FF - RR, FF - GG, FF - BB), where each component is given in hexadecimal. As an example:
color = (12, 4A, FF) complement = (FF-12, FF-4A, FF-FF) = (ED, B5, 00)
Adobe is using a slightly different definition from this "trivial" method of calculating complements. Perhaps it is more appeasing to the eye, or perhaps it aligns more closely with how the human eye works.
EDIT: Looking at this answer a few years later, I have to say that color spaces, monitors, and the human eye work in weird ways. This means that there is no one "correct" way to calculate complements. Your monitor can only display a certain range of colors, and the human eye is sensitive to certain colors more than others. This leads to many valid formulas to calculate complements.
As you can see, there's a fair amount of gap between 460 - 500nm, leading to a different human perception of expected color mixing than what is shown using actual scientific measurements.
I believe there are certain color spaces which allow for linear additive color mixing that matches our expectations...?
Here, I made a small quick web "app": http://jsfiddle.net/rXsAT/
Looks like someone already made a nicer version.
This is a rather complicated subject involving a bit of chemistry, biology, and physics.
Just know that additive color mixing with pigments is fairly different from light.