Have you ever downloaded a texture pack which makes minecraft a horrible rainbowy mess? no? Would you like to?
It even makes the lighting and sky a rainbowy mess IF you use optifine:https://www.optifine.net/home, otherwise you can turn clouds on for a similar rainbow sky effect.
Some parts of the pack work in 1.13+ - and the rain seen here works in any version! 
Best used in versions lower than 1.13 but some bits work all the way up to 1.16.2
Most features do not need optifine but I would still very much recommend using it for some of the cool lighting/sky effects.
Also it looks best with smooth lighting on.