When printing numbers on white decal paper, if you want a white outline, it helps to have a thin black outline as the "cut line".
If you are using Power Point as you artwork program, you can make this outline by stacking up three copies of your number:
on top is the main number, in black (or some other color)
Behind that, make a copy of the number that is big enough to give you the the white outline
In the back, make a copy of the white number, and make it just a hair bigger, and make that the color you want the cut line to be.
It helps to do this on a light color background, like a light grey.
This isn't the way I do artwork, but I have a more expensive artwork program, that makes this very easy.
You can get laser printers that print white, but you need to be prepared to spend at least 10 times as much
as you spent for the laser printer you have!
VSRN