This class supports drawing a Label without background.
The Problem is: A swt.Color doesn't support the transparent/opaque/alpha property of colors.
Therefore setBackground(Color) with an non-opaque color can't be used in SWT (in the current version).
But a swt.widgets.Composite support drawing without background.
This class isn't offer in the Gral interface. It is used for Prompt labels which overlay an input field.