I've been playing with the Tweak Tool in an effort to create something sparkly, like a Disco Ball (but not really).
I've given the array of objects some colour then used the Tweak tool to jitter the Luminance. The problem I have is that the jitter effect doesn't come close to covering the full spectrum of luminance values. So the result has a distinct lack of contrast and looks more matte than sparkly.
With maximum pressure the range of jitter always pulls towards the middle of the spectrum and instead of getting a range of values between 0 and 255, I get a range between 90 and 150.
I find this is true for saturation also.
Here's an example (http://yfrog.com/7gjitterrangep): http://www.nabble.com/file/p24178629/jitterrange.png
In this picture I started with very light Cyan on the left and very dark cyan on the right (for illustrative purposes). I then used the jitter tool with luminance and saturation modes. The result is pretty much the same for both groups with a relative small range of variance.
I may not be thinking correctly about how this feature works. I imagined that greater pressure would create more variance in the spectrum. But it seems like the more pressure you apply, the more it shifts towards the center of the spectrum, but the variance is contained.