A diamonds color refers to how colorless a diamond is. The Gemological Institute of America (GIA) grades diamonds on a scale from D-Z. D,E, and F make up the colorless range while, G, H, I, and J make up the near color less range. The closer you get to D, the more valuable the stone is. The difference between colors is very subtle and can be difficult to see from an untrained eye, however the slight differences make a big difference in value and price.