Opponent colors

There exist three opponent color pairs:
Light-Dark;
Red-Green;
Yellow-Blue.

We cannot have something that is both light and dark, or red and green, or yellow and blue (but we can have reddish-yellow (orange) and blueish-red (purple), etc.). The two colors in each pair are totally opposite or exclusive. This fact enables us to establish LAB, a 3-D color space, in which these three pairs are the three axes.

Structure below shows the relationship. The diagonal colors are opponent pairs:

     (O)
    R - Y
(M) |   |
    B - G
     (C)

       (橙)
      红--黄
(品红) |   |
      蓝--绿
       (青)

It seems that there should be four basic or root colors (RYBG), however Y can be produced by mixing R and G (this makes sense as Y resides between R and G in spectrum, so the overall response from eye cone receptors is yellow) so Y is not a primary color.

Anyway, opponent colors are very mysterious to me.

Opponent colors appear in our afterimage or ghost image, which refers to an image continuing to appear in one's vision after the exposure to the original image has ceased [2].

Are opponent color pairs the same as the inverse colors in the negative film? I don't think so. The three primary colors in negative film should be CMY.


References:
1. Bruce Fraser, Chris Murphy, and Fred Bunting, Real World Color Management, 2nd ed. Peachpit Press 2005
2. www.absoluteastronomy.com/topics/Afterimage