Today’s Question: For monochrome images ready to print, will any shade of gray ever be out of gamut? If not, do various rendering intent settings actually do anything at all, or will all produce the same print?
Tim’s Quick Answer: No, the gamut warning won’t be useful for black and white prints, at least for any normal printer. Put simply, all shades of gray will be considered to be within the gamut of any normal printer.
More Detail: When it comes to producing a print, the overall color and tonal values in your print are essentially “mapped” based on the behavior of the current printer, ink, and paper combination. White in the image will be translated to the color of the paper (meaning no ink will be applied), and black in the image will be translated to the darkest value the printer is able to reproduce.
All of the shades of gray in between are therefore going to be within the capabilities of the printer, since they fall somewhere between black and white and don’t require any color. You will generally only find that colors fall out of gamut when they are very highly saturated, so that the color goes beyond the saturation level of the inks being used to produce the print.