haha, thanks weaselhammer.
Best suggestion I can make; and I've done it a couple of times with great success, is to use a two part decal application.
If your design isn't terribly complicated, you print out the color that you would need on regular decal paper, and then print out an outline of what you need in white onto the white paper.
For example:
On this Army Air Corp decal:
I would print out the color portion on clear decal paper.
Then I would print on the white decal paper the outline of the star so I would know where to cut; alternately you could just cut out a circle for a richer color.
Then it's a matter of placing the white portion onto the surface and let dry.
Coat that with a layer of clear.
Then place the color portion on top of the white and voila!
Edit: I should preface this that this is a technique where printing entirely on white paper is not feasible; such as instances where opacity is required and clear decal paper is needed.