If I'm understanding this correctly, a particular shade of green has no inverse? Or perhaps it would be better to say it's inverse is the same value. Like how sine and cosine intersect at the square root of 1/2.

Complementary colors are pairs of colors that are of “opposite” hue in some color model. The exact hue “complementary” to a given hue depends on the model in question, and perceptually uniform, additive, and subtractive color models, for example, have differing complements for any given color.

In color theory, two colors are called complementary if, when mixed in the proper proportion, they produce a neutral color (grey, white, or black).
In roughly-perceptual color models, the neutral colors (white, greys, and black) lie along a central axis. For example, in the HSV color space, complementary colors (as defined in HSV) lie opposite each other on any horizontal cross-section.
Thus, in the CIE 1931 color space a color of a particular "dominant" wavelength can be mixed with a particular amount of the "complementary" wavelength to produce a neutral color (grey or white).
In the RGB color model (and derived models such as HSV), primary colors and secondary colors are paired in this way:
red and cyan
green and magenta
blue and yellow