Building Desaturation from scratch.

Mike wanted to make a blend mode like the "Color" mode in Photoshop and asked me for help. But, considering the fact that the people at Epic haven't already made one, it might be a long shot. I learned about Relative Luminance while researching this, so now I know how the desaturate node works.

This was the only resource I could find on the subject and, at a glance, seems doable in Unreal. Hopefully I'll have enough free time to try it out.