GrayPaint (also spelled Gray Paint, GrayPaint?, Graypaint, etc.) is a raster graphics editor for Palm OS. Its native images are 16-shade grayscale, and may be found in a Palm OS Database file named GrayPaintDB.pdb.
GrayPaint is, we have to tell you, an exceedingly difficult format to Google for (or search for in any other search engine competing with Google®). You end up with listings (native and paid) for various physical paint companies advertising the gray-scaled varieties of their products, and attempts to refine the search eventually get you to treatises on doing gray-scaled images in various computerized paint programs, as well as a conversion program in Visual Basic that happens to be called "Graypaint", but only converts established image file formats rather than inventing its own.
Based on the demo GrayPaintDB.pdb file, we're assuming that GrayPaint PDB files have ASCII "
DATAGrP?" at offset 60. (The last character is a literal question mark, not a wildcard.)