When monochrome PBM or monochrome BMP is specified in (Property Sheets->[Graphic]->) -GIF: for PostScript color image files, the Preview is in black and white using gray scale even if the original image is colored.
When monochrome PBM is specified for monochrome in the [Graphic] of Property Sheet, the file name created by Ghostscript is different than the one for color. Therefore, both files can remain without overwriting.
Although more space in the hard disk is required, it would be useful to use both monochrome and color appropriately depending on the situation.