Allows you to get or set the gray level.
Grayscale levels can range from 0 (black) to 255 (white).
Querying this property does not change the ColorSpace. This means you can obtain
approximate Grayscale values for RGB or CMYK colors.
However if you change the value of this property the color will
automatically be converted to Grayscale.
This property can also be used to specify levels for spot
colorants. Levels can range from 0 (0% intensity) to 255 (100%
intensity). See the AddColorSpaceSpot
method for an example.