Complementary color:
- A color directly opposite to another on a color wheel and providing the greatest chromatic contrast to it.

see table at: [link]

red & green
blue & orange
yellow & purple
The complement of each primary color (red, blue, or yellow) is roughly the color made by mixing the other two in a subtractive system:

red complements (blue + yellow) = green
blue complements (red + yellow) = orange
yellow complements (red + blue) = purple
When two complements are mixed they produce a grey or brown.

The use of complementary colors is an important aspect of aesthetically pleasing art and graphic design. This also extends to other fields such as contrasting colors in logos and retail display. When placed next to each other, complements make each other appear brighter. On an artistic color wheel, complementary colors are placed opposite one another.

So here you go:

Red and green (by far the most popular complementar contrast in photography):



Blue & orange:



Yellow & purple (the most hard to find):