my first question here,

My question is the following: If im rendering a cube with a single lightsource with the standard white/grey diffuse-shader, therefore getting a picture with values-only and then multiplying a color on the image, the color on the different surfaces just changes its brightness. (obviously)

But when im giving the diffuse material the color i have multiplied on the first render, in the new image the color just doesnt change its brightness, but also its saturation.

So my question is: Why? Is there just a simple difference i didnt recognize? 1st picture: Values multiplied with color. 2nd picture: Used the color as material for the diffuse-shader.