[alpha_squared]

I got 14/20 on my first try just by knowing how the color mixing works. A few simple rules:

- Higher values mean brighter colors

- The closer the individual colors are to each other, the closer to "gray" it looks

- R + G = Yellow, R + B = Fuchsia, G + B = Teal

[Kim_Bruning]

The typical sets of primary/secondary colors are RGB and CMY. Which set is considered "primary" depends on if you're doing additive (light) or subtractive (ink/pigment) mixing.

In additive color mixing, Red (#F00), Green (#0F0) and Blue (#00F) are the primary colors, and Cyan, Magenta and Yellow are the secondary colors.

Cyan: Green+Blue (#0FF)

Magenta: Red+Blue (#F0F)

Yellow: Red+Green (#FF0)

[stavros]

You also need to know the combinations, for when you get, eg, 0FF. Though I was once asked to find 0FF and the choices also had 1FF in them. Obviously it was pure luck.