CMYK is a subtractive color model used in color printing. It is based on
mixing pigments of the following colors in order to make other colors:
C = cyan
M = magenta
Y = yellow
K = key (black)
Submitting your files in CMYK color mode will give you the best results. If
you submit your files in RGB or any other color standard, they will be changed
to CMYK during preflight. Because only half of the colors in the RGB standard
can be exactly matched in CMYK, conversion will cause the colors to shift.
If you are concerned about color and your job is color critical, please order a hard copy mail proof to ensure color accuracy.