Hi Robin,
I found this really useful company about six months ago.
If you go to this web site....
http://www.paints4u.com/AutoColours.aspx?ProductID=5020
You can put in details of the car you have seen (make, model, year, basic colour like 'green', etc) and it'll show you the manufacturers colours used!
You can even order a spray can to see if you like the colour before you start!!
Mind you it doesn't help you make up your mind if you are like me... (it's going be Red, or maybe white, or dark green or dark red, and silver looks nice but what about black or maybe old english white with black wings, etc etc...)
good luck,
...peter