The standard emitter has separate settings for birth rate in the editor view and for the rendered output. Is it possible that you increased the editor output but not the render output?
As for random color, there is a way to do it. Basically what you would do is use a cloner to generate the particle geometry instead of the emitter. Set the cloner to object mode and drag the emitter into the object link box. Then assign the cloner a random effector with color mode turned on. Instant random colors.