Some of my custom GUISkin setting only work with Pro Skin

Hi, I have a trouble with my custom GUISkin of editor, some properties of my guiskin only works with Pro Skin, but I wan't to work with Light Skin.

Currently, this is an example of my interface:

But I change to light Screen, the green panel panel background only draws as white color:

Why? It's a bug or a feature limitation of light Skin?

Help much appreciated