The colour grading scale varies from totally colourless to light yellow.
The differences between one grade and another are very subtle and difficult to distinguish.
D-F: Colourless: perfect or almost perfect colour.
G-J: Near colourless: good to very good colour and this diamond may “face up” colourless when mounted, especially in white gold or platinum.
K-M: Light but noticeable yellow or brown tint. Not recommended for larger diamond stone purchases, especially in engagement rings.