Is there an equation to easily convert a color to its matching color in another hue?

I am trying to design a site with a couple color schemes. I am looking for a way to make color schemes that match mathematically.

For example, I know that #FF0000 matches perfectly with #00FF00 and #0000FF. Is there some kind of equation to get, for example, the yellow version of #509cc0? I also have the RGB values and the HSL values on hand.

Answer

I'm wary of purely mathematical approaches to color harmony; numbers have no aesthetic sensibilities. That said, since the Hue wheel is divided into 360 degrees, one can build a complementary color scheme by adding 180 to the hue for any given color, a triadic by adding and subtracting 120, and so on.

The triadics below were done using simple arithmetic in the H field of the Photoshop color picker, adding 120 to the value each time. Pure RGB above (in reverse sequence, sorry!), and your starter color, #509cc0 in the row below.