Gradient map

https://docs.unrealengine.com/latest/INT/Engine/Rendering/Materials/Functions/Reference/Gradient/index.html

https://forums.unrealengine.com/showthread.php?1845-Is-there-a-material-function-that-works-like-Photoshop-s-Gradient-Map

http://artisaverb.info/DitchingDiffuse.html

https://realtimevfx.com/t/particle-gradient-mapping/1952

http://technical-eden.blogspot.kr/2012/01/gradient-mapping-awesome-way-to-get.html

http://blog.lostmountaingames.com/unreal-engine-4-particle-gradient-mapping/

Motion Vector & 2D gradient lookup Shader 

A Game of Tricks III – Particles fun (part1)

http://www.alkemi-games.com/a-game-of-tricks-iii-particles-fun-part1/