What if I want the color within the margins to be different from outside the margins. How do I do it?

You can't.
margins are the space around the outside of the element so will be whatever the background colour/content of the parent element is.

Of course there are ways such an effect can accomplished.

Well,, there are sites out there that look there is a different color outside of the margins

<same topic so two threads merged>
I'm very new at CSS. I visit sites that use CSS and it looks like they have color within the margins they set that are different than outside the margin. How do you do that.

Sure and they probably use sized and overlaid elements.

or a thick, colored border

ok look at this site http://www.csstea.com/index.php?start=42 Where the content is, its white, on the outside of that is a different color. That's what I'm trying to understand

10px wide border plus a heading at the top with a background the same colour as the borders.