Okay, let me try...
If Roger goes back a few years BP (Before Peep), he, like me, was working on comics that used the letterpress system of printing, which basically relied on a maximum of four colours of ink to produce all pages. Black was the starter, of course, and the only one needed for most of the comic pages back then.
Add in red, and you could produce what we called 2-colour pages, which actually provided you with a small range of colours when you factored in stippled (dots, rather than flat colours) strengths of the red and black inks, and you could create a brown effect.
Throw in blue and yellow, and you have a proper full colour Bash Street Kids spread!
Eventually, the letterpress comics were all replaced by 'photogravure' presses, printing much more vibrant colours on glossier paper, making the comics look more like magazines. Essentially still using those four inks, but calling them Cyan, Magenta, Yellow and Key (black), just link yer modern inkjet home printers, and allowing for much more versatility (shades and gradients) in the coloured artwork.
Online, there are no limits though. I colour directly onto a screen these days, using the RGB (red green blue) mode, which offers you literally millions of colours to select from, especially if you are publishing the results on screen. If the work is to be used in print, however, some of the more vibrant screen colours aren't available. So, if I want to check, with a couple of clicks, I can convert the finished work into CMYK mode, and it will show me how the same image will look when it's printed on paper. It's usually pretty close, but some of the colours might be a touch duller. It rarely causes any problems though, and I usually leave that to the features desk people to worry about, and don't even check.
Just read all that back, and I'm quite impressed that I sound like I might know what I'm talking about.
