Bottom colors of Soviet submarines

[fred tannenbaum]

Dear friends:

In viewing completed kits of Soviet submarines on sites like SteelNavy.com and Modelwarships.com, the bottom paint color on the boats ranges from slate gray, lightish green and of course, red.

Is there a single color or did the bottom color vary between submarine classes?

Thanks for any guidance and enlightenment!

Very sincerely,

Fred