Create a custon material / shader to implement a grayscale filter

I have researched a lot and I managed to get a texture to become grayscaled. I am very new to shaders but I can see how if it’s possible to achieve glass effects with some colors it has to be possible to achieve what I am seeing in this video:

Any hint or example of how to achieve this or any path to keep the research would be really appreciated. The problem right now is I am not really understanding how to modify the color that the shader gets by transmission. I learned how to make the change with a texture in the link I shared before and I think somehow the key to get the colors is inside of this shader from drei:

but to be honest I am still not good enough to figure it out.

any help would be really appreciated

have a nice one

Maybe this will be useful somehow:


Effect composer with custom postprocess shader overlay