The home-made inkjet decals only work on a white truck if you're using the clear decal paper. If you use the white decal paper, you can use them on other colored trucks, but you have to trim all around the decal so none of the white shows through.

Mike - I've tried to email you directly three times about decals but my messages are kicked back. Email me and we'll discuss decal making. I would not recommend the Testor's Decal Starter Kit, as the paper is crap and often very old. In addition, some printers, like mine, do not set up the color Red properly and it often never dries properly. Color Laser printers are the only way to go! Fast, cheap, clear and crisp and no additional sealing is needed.