Check out
http://www.mustangii.net/1975/75colors.asp.
It shows a paint chip along with the paint code. If you check your data plate it should have a paint code on there, it will help you locate the proper color. If you can't find it, post it here and I will see if I can find it for you.
by the way,
www.mustangii.net looks like a good source for info on the Mustang II. There are not a lot of sources for the II's. Good Luck!