4 color printers have Cyan, magenta, yellow and black
6 color printer have the same plus LIGHT magenta and LIGHT cyan.
A color printer doesn't mix colors to produce other colors
When you see orange come out of a color printer.. its actually tiny drops of magenta beside tiny drops of yellow... your brain it tricked into blending the 2 colors because the tiny dots are so close together
By using lighter verions of magenta and cyan, the printer can produce lighter, more subtle shades than are possible with the standard cyan and magenta colors.. hense, you get more "real life" colors
i hope this helps