   HSL Colour Space in DirectX
  I'm doing some post processing techniques on a scene in directX and I have a simple tint effect that tints the screen red gradually over time then resets. I want to change the colour passed to the shader using the HSL colour space rather than RGB. Is it best to convert from RGB - increase, for example, hue, then convert back to RGB??thanks   
  Well, you've got a tradoff here.You can pass all your colours to the gpu in HSV - but that means converting all your textures and vertex buffer colour data, which can take a long time.Converting in your pixel shader is of course expensive, but there is an alternative. You could encode both conversions in a seperate volume look-up texture. You get HSV by indexing with RGB, and the other way around. This way, your performance hit is only 2 texture look-ups and some scaling and biasing.this is probably what you are looking for :  GPU Gems Colour control, for free .   