when you got open whatever image app, like fireworks, photoshop, paintshop or any other that gives hex FF FF FF or decimal 255 255 255 RGB values, if your app has Hue Sat and Luminance, pick a colour you really like, then right the sat value down, now whatever colour you pick say you got a nice red in the first place, and now you have a blue type the sat value you noted and hit enter, you now have to perfectly matched colours, dead dead easy....
further to that... for those who don't know,
hue = colour (reds greens blues yellows etc)
saturation = strength, kinda like amount of colour/white mix
luminance = kinda easy no?
oh and some programs have alpha channels (unrelated to colour matching) thats the transparency