If I have an OpenGL texture, and I need to perform HSL modifications on it before rendering the texture, from what I've heard I need a shader. Problem is, I know nothing about shaders. Does anyone know where I would need to look?

I want to write a function where I can pass in a texture and three values, a hue shift in degrees, and saturation and lightness multipliers between 0 and 2, and then have it call a shader that will apply these transformations to the texture before it renders. The interface would look something like this:

procedure HSLTransform(texture: GLuint; hShift: integer; sMult, lMult: GLfloat);

I have no idea what's supposed to go inside the routine, though. I understand the basic math involved in HSL/RGB conversions, but I don't know how to write a shader or how to apply it. Can someone point me in the right direction? Delphi examples preferred, but I can also read C if I have to.