Hi Wakeguy
I've attached a VI that uses a tank with 3 sliders. One for the level and two for the limits. The limits use a "No-Fill" fill style if you check the control's properties and have been set to black. All three are in a loop just to show how they can be altered dynamically. VI is version 7.1. I have noticed problems when changing the slider colours which could indicate a LV problem with this control.
Hope that helps
Neil