GrayLevel[level] is a graphics directive which specifies the gray-level intensity with which graphical objects that follow should be displayed.
The gray level must be a number between 0 and 1.
0 represents black; 1 represents white.
On display devices with no native gray-level capability, dither patterns are typically used, as generated by the PostScript interpreter.
See Section 2.10.1 and Section 2.10.3.
See also: RGBColor, Hue, Raster.
New in Version 1.