Hi there,
I created a particle system, using a custom material and only one max. emission (i want to create some kind of shockwave).
these are the settings for the particle system.
for some reason, the particles are always white only 
what do I do wrong?
Well, the first thing I would look at is the Energy, it is analogous to lifespan, and it is set to 1 second.
I believe the color changing is happening but is being over shadowed by the two steps of white at the end of a particle’s life.
Stretch that time out and let them get away from each other a bit.