wildfire4 config.pro option documentation for: TIFF_TYPE            

tiff_type

palette, rgb, grayscale, mono

determines the type of tiff items that are exported and identifies the color to use. shaded images are exported to the tiff format as 24-bit rgb images, by default. palette color (level 3) mode is also supported.

you can set tiff_typeto any one of the following values when you select tiff as the plotter type:

• palette—8-bit colors

• rgb—24-bit colors

• grayscale—gray scale colors

• mono—black and white