Open the driver's side door. On the main body there will be two little metal tags; one will have the serial number of the car, and one will have the paint code, which will either be a three-digit or a four-digit number (usually four-digit). Tell us if you don't have the tags.
Paint codes are here:
http://www.willhoitautorestoration.com/paintsamples.php
Note: you can always get data pertinent to your car through Porsche's Certificate of Authenticity (COA) program.
http://www.356registry.com/techinfo/research/kardex.html