What is the highest grade in diamonds?

The highest grade of diamond falls into four categories:

• Clarity -- Flawless or Internally Flawless.
• Colour -- "D" colourless, or Intense Vivid Fancy for a coloured stone.
• Cut -- since the cut is determined by the previous categories, if the stone is of the highest rating for those, then the cut must be near perfect.
• Carat weight -- This is determined by all three preceding categories and the goal is to make it as high/ heavy as possible.