The classic scale runs from the colourless diamond (D, the rarest) to the diamond historically called "Cape", a trade term originating from the old Cape mines in South Africa, used for slightly more tinted stones. The closer to D, the rarer the stone, and the higher the price.
Give me a range rather than a single choice, it helps me find you the stone with the best value for money.
For inspiration: your ring will be hand-made to order whichever style you choose.