Printing a white illustration

As others have said, checking with your printer is your best bet. In this case, I work for a printer, and customers supply white art in several ways. My two favorites are either Black as described above, or as a custom spot color labeled "MUST PRINT WHITE".  My least favorite way is to have the art arrive using Pantone Trans White, since that tends to just confuse everyone.

Your basic consideration boils down to this: whether you are providing a file to be reproduced using process color or spot color.

Process color means using a small number of "primary" ink or dye colors to simulate other colors by visually "mixing" them (actually by printing them as arrays of tiny dots or lines on top of each other).

Spot color simply means loading a particular color of ink, dye, paint, resin, vinyl, foil, or whatever substance the particular repro method uses that is already the specified color. The resulting color is simply a matter of what color the substance used in the reproduction method is.

You can't create white by mixing primary colors of ink or dye or paint because inks or dyes of any color are already darker than white. They get their color by reflecting only a portion of the light that falls on them; so mixing them is a subtractive color process. You don't get white by subtracting light.

So since you specifically say you are designing for decals on which the artwork will be white and printed on a clear substrate, that implies spot color. Whatever substance is being used for the image, be it ink, paint, vinyl, or anything else, that substance is already white.

So you can simply provide the artwork (the image) as black, with instructions that the image is to be reproduced as white. The resulting color is simply a function of what color the substance used in the reproduction method is.

JET

It is best to check with your print vendor to find out how they want illustrations submitted. However, I would make the text black and let the printer know, in writing, that the text should be printed with white ink.