I have a bad tendency to use the terms "color", "pen", and "register"
somewhat interchangably.

From this point forward, I will be adopting the following:

   "Pen" - Will be used to denote one of the physical "slots" which can
           can hold a single set of RGB values.

           For example, if you have an 8 color screen, you actually have
           8 pens available.  Each of these pens can hold a different
           color.

   "Color" - Will be used to denote a distinct set of RGB values, which
             may also have a name at times (like "light blue").

   "Register" - The same as "Pen" in my book.  I will try and use "Pen",
                however, as Commodore uses this term.