Paint codes, as defined today imply a formula that says what percentage of what colors are mixed to produce a particular color. These codes are used universally by practically anyone to reproduce a color.
Honda did not make paint codes in this manner. It was just a code for their color, at least not until the 80's....so r-2c-c is a honda paint code for candy tone orange but that code is not a formula.
So, you need the Honda tank colors. Google your model, or vintage Honda motorcycle paints, parts book, etc....there are companies that reproduce those Honda paints......I know one source, call BOB's Indians in etters,pa. He can tell you what a 67 cl90 had for tank colors...I'm sure others on here can also...