Hi Ted
The little picture in the colour dialogue should let you know what changes.
But basically, the 2 background colours are the colours you then see in the
background styles drop down on the Design tab, and the text colour will
change (unless you override it on the master) depending on which you pick.
The accent colours are the colours used by drawings, charts, SmartArt, etc.
Hope that helps. If you have a more specific question, or are coming up
against a problem, let us know.
Lucy