The PostScript driver is a one bit-per-pixel device. However, this does not mean it can represent only black and white. Bitmaps in a one bit-per-pixel format can use any color for the foreground and background.
On black and white devices, colors are converted to gray levels by the PostScript color machinery. For example, when a bitmap is transferred to the printer, the foreground and background colors are examined to determine the two colors to use for the transfer.
Windows uses brushes to fill objects. Patterned brushes are defined by an 8x8 bitmap that is used to tile a region that is to be filled. However, since the PostScript driver is a one bit-per-pixel device, there is no color information stored in its brushes. When a brush is used to fill an object, the current text and background colors are used.
In Windows 3.1, the user can force all colors (other than white) to print as black by setting the All Colors to Black option in the Advanced Options dialog box. This option is useful if a printout loses detail from thin, light-colored areas.