Have a look at how I configured this slider:

This is just an example. Of course you can use colourful patterns or colours as the sliders background, but as you can see, you can also draw some lines (ruler-like) ('slider-lines.iff' in the CoolMUI archive, dir 'slider'), which give the sliders an impression of a additional functionality when adjusting the slider-button. I have used a MacOS-like style here by choosing a blue colour (R:168 G:210 B:255) for the slider gadgets. (Also don't forget that you can also choose a frame for both the slider frame and the button aswell as a font.)