Thanks!
American Blue/British Blue (aadd) actually have a wide variety of acceptable coat colors from powder blue to slate grey.
Russian Blues (rbrb) are a dark blueish grey with almost a metallic sheen. Russian Blues are also ticked in various shades of blue.
They are two different lines of blue. Much like breeding an Albino to a Piebald Ball Python. Two visuals will create non-visual double heterozygous offspring. Once you breed their offspring together you will create visual offspring carrying both the Russian Blue and American Blue genetics. They are called Russian Silvers (d/d rb/rb).