Change the color of particles on one side

how can you change the color of particles on one part of a particle system, like shadows on the bottom of a cloud?

 

hmmm... that's an interesting concept. What I would try, is rather than changing the particles colors, use a particle texture that has the shadow on it and play with the blending mode options. I'll think about it some more and give you some other ideas if I come up with any.

 

ok, how would i do that? and what about these UV animations on the particle renderer?

 

You may have a look at that one http://forum.unity3d.com/threads/56878-ParticlClouds-Package-v2-%28Volumetric-Clouds!!%29

It does exactly what you asked for.

 

well, i cant use anything pre-made, because were going to sell this

 

This is actually fairly simple.

Create an emitter. That is your "cloud".
Create a Bounds
Set the Bounds Max and Min to the emitter position.
Roll through all the particles.
use the Mathf.Min(Bounds.min, ParticleEmitter.particles.position) and Mathf.Max(Bounds.max, ParticleEmitter.particles.position) to set your bounds.
This gives you a Bounds.size.y, a Bounds.center.y+Bounds.extents.y and Bounds.center.y-Bounds.extents.y

Now just roll through the particles again, and check where they sit top to bottom.
Adjust the color of each particle using ParticleEmitter.particles.color to the Color.Lerp(bottomColor, topColor, (ParticleEmitter.particles.position.y - BoundsMin) / (BoundsMax-BoundsMin))

Tada, volumetric cloud....