Text substitution and change cell background colour. Numbers & AppleScript
I offer this with the disclaimer that I am unable to test this, as I do not use Numbers. However, with the help of this page, I am proposing this code as an example of what might help you achieve your objective:

        repeat with c in cells of column "B"
            if value of c contains "TRUE" then
                set value of c to my SUBSTITUTE(value of c, "TRUE", "RICHTIG")
                set background color of c to {0,65535,0}
            else if value of c contains "FALSE" then
                set value of c to my SUBSTITUTE(value of c, "FALSE", "FALSCH")
                set background color of c to {65535,0,0}
            end if
        end repeat