This isn't correct. The color space is horseshoe-shaped and cannot be represented by a triangle of three additive primary colors. In addition, standard color gamuts tend to be quite a bit smaller than theoretically possible. Check out: https://secure.wikimedia.org/wikipedia/en/wiki/Gamut . This is why hi-def TV is defining extensions to the usual colorspace.
Furthermore, the laws of physics don't particularly care that humans perceive three color dimensions, and surfaces and lights are allowed to absorb or emit whatever wavelengths they please. When you have a light source with a funky spectrum, this can cause colors to look very strange, as a surface might not reflect a funny, spiky spectrum the same way (w.r.t. the human 3-dimensional color space) it will reflect a smooth color spectrum of the same color. You've probably seen cars seemingly change color when the light source is primarily those orange-ish streetlights. My parents' red minivan, for instance, turns a red-tinted grey.
Furthermore, the laws of physics don't particularly care that humans perceive three color dimensions, and surfaces and lights are allowed to absorb or emit whatever wavelengths they please. When you have a light source with a funky spectrum, this can cause colors to look very strange, as a surface might not reflect a funny, spiky spectrum the same way (w.r.t. the human 3-dimensional color space) it will reflect a smooth color spectrum of the same color. You've probably seen cars seemingly change color when the light source is primarily those orange-ish streetlights. My parents' red minivan, for instance, turns a red-tinted grey.