Olivetti D-COLOR P26 - Manual (Page 40)

A Guide to printing> 40
4. From the [Feature Sets] menu (3) , select [Colour
Options].
5. From the [Colour Mode] menu (4) , select [Greyscale].
6. Select [Always Use Printer Halftone] checkbox (5) .
This ensures best quality when using greyscale.
7. Select the [Use optimized greyscale halftones] checkbox
(6) .
This may slow down printing slightly, but will produce
superior results.