I've a set of same coloured tiles I want to use the tweak to jitter the lightness of. With just the lightness option toggled, the tool pushes the colour lightness towards the centre of the lightness scale. Even if you start with a very pale color it'll move towards middle, and likewise with darker--it always shifts away from the extremes.

I'm using a tablet and more pressure does make a difference, but not to the point where I can get high contrast. Setting the force to 100% doesn't make a dramatic difference.

I was hoping to get a result that has more sparkle.