Diamond colour grading...
Acting as a prism, a diamond can divide light into a spectrum of colours and reflect this light as colourful flashes called fire. Just as when looking through coloured glass, colour in a diamond will act as a filter, and will diminish the spectrum of colour emitted.
Most diamonds look white, but there are many subtle shades. The closer a diamond is to colourless, the more valuable it becomes. Diamonds with no hint of colour at all are very rare, and are called colourless. Grading laboratories use a colour scale that ranges from D (completely colourless) to Z (strong yellow).
Diamonds ranging from D to F in colour have virtually no colour tone and are the most valuable. Diamonds in the range of G to J are almost colourless and most people cannot detect colour tones in them, they are less expensive. Diamonds of K colour and lower have enough yellow colour tone which most people can easily detect, nevertheless, these stones can still make fine jewellery and their cost is much less than higher colour grade diamonds. While many diamonds appear colourless, they may actually have subtle yellow or brown tones and these colour grades include P and Q. Although still beautiful, they will be less rare and therefore less valuable. To appreciate the simple beauty of each individual stone, you should compare diamonds side by side.