Diamonds are not all truly colorless, but it's the colorless, often called white, diamonds that other shades are judged against.
In nature, diamonds are found with a wide array of color from colorless, faint yellow or brown, to rare pinks, blues, greens and other colors known as "fancies." Most diamonds have at least a trace of yellow, brown or grey body color. In general, the more colorless a diamond, the greater its relative value. A totally colorless diamond allows white light to pass effortlessly through it, creating a rainbow of colors as the light is dispersed.
If the diamond is certified the color of your diamond will be reflected on your certification from the GIA.
If your diamond is not certified you can determine the color of the stone after cleaning by placing it on a non reflective white background. To accurately reflect the color the stone should be loose so it is not influenced by the metal around it. Selecting a diamond color is a matter of preference. Fancy yellow and pink diamonds make a creative and individual statement for an engagement ring.