As far as new models go, I believe that is correct, that the 301 was the last new model offered in classic black. I’ve never seen a black 400 series, and I don’t think they were offered in anything but tan and cream. At least at the Anderson factory.
If you’re putting together information on your machines you might enjoy this site,
http://www.mysingerstories.com/
You can enter your serial number for machines built before 1970 and receive a pdf certificate.