The best color in a diamond is no color at all.The best color is no color at all. A completely colorless diamond acts as a prism or lens, it will disperse light into a rainbow of color.
Colorless diamonds are the rarest and are highly valued. Most diamonds used in jewelry are nearly colorless with slight tints of yellow or brown. Color is judged by comparing the diamond against a master set of grading diamonds.
For the layperson, color is judged by viewing the diamond against a white background in natural daylight. Fold a piece of paper and view the diamond from the side. The diagram above shows the differences between color grades.