Colour rings & colour codes are yet another thing about this industry that are not standardised.

Different colour manufacturers produce their own colour rings & codes.
The same manufacturer can eg Garnier or Wella, use different codes for the same colour depending upon what country you in.
The codes also vary depending on if your referring to men's hair or women's hair.

I'd only recommend getting a colour ring if you plan on using that supplier regularly, otherwise its a waste of money because it possibly won't be relevant to future orders with a different company.

Some companies offer a colour ring with an added charge, thats refundable once you've returned it with your first order.
That seems like a good idea to me.