Hi Strahobrz -
Sorry misunderstanding your terminology with the particle systems. A Mesh emitter is what I thought you were dealing with, but for a default sprite particle system RimmyD is correct the material itself was your problem.
Here is what the default material should look like:
The Particle Color node will allow the Color Over Life default node to add color to you particles in Cascade as well as set their alpha (transparency) value.
Thank You
Eric Ketchum