In the diamond rating scale, IJ refers to the color of the diamond, while I2-I3 indicates the clarity. IJ diamonds are nearly colorless. Diamonds with a I2-I3 rating have internal imperfections that are visible under 10x magnification, and these flaws may be visible to the naked eye.
The most valuable diamonds are colorless, with a color grade rating of D. Diamonds with an IJ rating fall into the second-best color tier: nearly colorless. Low-grade diamonds with a color rating of S-Z appear obviously yellow to the naked eye.
In the rating I2-I3, the "I" stands for "inclusions," or imperfections within the diamond. Knots, cavities and graining are common internal flaws. I2-I3 is the lowest grade of six possible diamond clarity ratings. The highest tier is designed by FL for "flawless."