Particle Image Backgrounds

I’m creating particle effects using the particle panel - but seemingly regardless of the blending options I choose, each particle image (which is a colored circle with alpha transparency around it) appears with a light gray-ish background. This is really killing the particle effects. Does anyone have any idea why this might happen?

I figure it could be configuration rendering settings, influence from lights, etc. I really have no idea but I also really need to fix this.