Originally published on:
Introduction to Shading with Complementary Colors
To find the correct complement, we need to know its hue so that we can find the opposite position on the wheel; in addition, for a complement to work well, it should have approximately the same value. If you look at the colour wheel above and compare it to your palette you will notice how the lighter and darker values are not represented. Since visually determining the appropriate complement is much easier than trying to work it out in your head (something I still have trouble doing) I have expanded the colour wheel to give an indication of value in addition to hue.
It should be possible to find a reasonable
approximation to most palette colours and the colour directly opposite and in
the same ring will be the correct complement as in the two examples. It's
important to remember this is the ideal situation, if you are seeking a
complement and you don't have a colour of the correct hue or value as long as it
is close it will still work reasonably well - this is why Cobalt Blue works so
well as a complement for many oranges and earth colours as you will see below.
Also remember you can mix a secondary colour of any hue you want if you have a
good selection of primaries, keeping the number of colours in your palette down
and money in your pocket.