Introduction to GLSL shaders

[Jarewill]

I'm looking for a way to turn the screen black and white. (kinda like the Reverse lightmap does, except not reversed)
I've been told that the best way to do this would be to set up a hardware shader, but I frankly have no idea how to do this.
If there are some good and easy to understand examples, I'd heavily appreciate them.

Also is there a way to toggle them on the fly?
Let's say a nightvision-like powerup that sets the map to full bright and enables said black and white shader.

[m8f]

Take a look at MariFX: https://github.com/OrdinaryMagician/marifx_m

[Jarewill]

Thanks for the link!
Found my answers how to set up a shader, activate it midgame and the hue and saturation shader was exactly what I was looking for.
Thank you Marisa for those shaders!