Try taking a look behind your dashboard or within your engine compartment. You can usually see what the original color was. You can then link to this page http://www.geocities.com/vwtyp181/181_2-4.htm
to figure out the actual paint code.
If you car is a 1974 THING, and that is a medium to dark green showing, the original color may have been 60F Avacado.
As chinacat mentioned, look under the dash for some original paint. The paint code was originally on a piece of paper and most, if not all are long gone.
Avocado green was the only green used on VWofA THING's and it only appeared in 1974. If you want to find out what color your car is now, assuming it wasn't green originally, you only have about 500 different shades of green to go though in the master paint color index.
Good Luck
[This message has been edited by BobMiller (edited 03-12-2003).]