For Printed Maps have always used CMYK (or C-CL-M-ML-Y-K for six colour printer)
So 100% Cyan 5% Magenta will be (C100,M5,Y,K)
Winner as Black = Black (great for maps text etc.)
http://en.wikipedia.org/wiki/CMYK_color_model (Subtractive Colour)
For Screen output (Like Web, TV or PDF) - Use RGB (Red, Green, Blue)
Black is more a mixture of all and is more a muddy brown.
Comparisons between RGB displays and CMYK prints can be difficult, since the color reproduction technologies and properties are so different. A computer monitor mixes shades of red, green, and blue to create color pictures. A CMYK printer instead uses light-absorbing cyan, magenta and yellow inks, whose colors are mixed using dithering, halftoning, or some other optical technique.
can also confuse the issue with RGB/CMYK
Pantone (specific to Printing - Pantone system also allows for many 'special' colours to be produced such as metallic's and fluorescent's)
Tend to work at CMYK then convert to RGB
BLUE (RGB is blue but CMYK cyan in ink)
CMYK 'K' =KEY for Key Plate represents Black not to be confused with Blue.