How could I find a color that complements another programmatically?

Given any (user selectable) color, I am trying to generate a matching color to go with it for a user interface.

Basically, it should be a color that is either similar, or complements it very well - but, it must also be easily distinguishable from the first color. So far, I have tried lightening/darkening the color, which works ok - but it doesn't look the best, I am not convinced that there is no better way to do it.

What are some alternative or better ways that I could achieve the desired effect? Any help is much appreciated!

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Side note - 开发者_StackOverflow中文版I have the color in both RGB and HSL formats, although could easily convert to others if need be.

Would it be possible for you to use this site below to help you reverse engineer the concept you are looking for?

http://colorschemedesigner.com/

It's flash so you can't see the code, it still might help though.

If you can figure out how to produce a colour wheel, then complementary colours are on opposite sides of the wheel.

Update

Wikipedia has useful pages on hue, hsl and hsv

http://en.wikipedia.org/wiki/Hue

http://en.wikipedia.org/wiki/HSL_and_HSV

and more on conversions

http://130.113.54.154/~monger/hsl-rgb.html