GrayScaleShader

This is a very simple, straightforward shader, which does not need any parameters or configuration.
It will render everything in grayscales using the multipliers [0.299, 0.587, 0.114] for RGB while activated.

To render a single object with this shader, use code like this in your Draw or DrawGUI event:

shader_set(GrayScaleShader);
draw_self();
shader_reset();

That's it! Now your object will look grayscaled.