Lighting will be a critical factor in grading color accurately. Negative factors in lighting and environment would include bright surrounding colors, dim light or direct sunlight. Ideal conditions would include neutral colored surroundings and natural daylight away from direct sunlight. For starters, a desk lamp with filtered, cool white, balanced, fluorescent bulbs would be effective. To eliminate ultraviolet light, place a piece of Lexan polycarbonate over the bulbs. Along with good lighting and a set of master stones, the grader himself is the most important component. Even the most experienced graders will at least use master stones for more expensive purchases and will make sure there is more than sufficient light before making an offer based on their grade.
After the lighting issue has been dealt with, the next step in preparing yourself to do actual color grading, is to practice on loose diamonds. Some pros claim they can grade color without the aid of master stones. On the other hand, some say that diamond color grades are impossible to memorize accurately. Dealers with years of experience (and an aptitude for color grading) can come very close. When dealing with very valuable diamonds, even they will likely use master stones to verify their judgment before making an offer.