Learn about Gemstones
Color is the primary factor when evaluating a color gemstone. The tone and hue of color you should look for will depend on the type of color gem you choose. If the gemstone is blue as in a blue sapphire, avoid "overcast" shades of grey or green.
For rubies, the ideal color is "Pigeon's Blood Red", thus a tendency towards pink will devalue the ruby.
Green emeralds should avoid yellow. Thus, a deeply saturated color and true hue of the gemstone is what will set it apart from the rest. In addition, look for an even distribution and purity of color when viewing the gemstone face up.
It is important to note that a color that appeals to you may not be the recommended color for that specific gem. Find a color that appeals to you, you are going to be the one enjoying it!
Clarity is less of a factor when evaluating a color gemstone. The amount of inclusions a color stone possesses depends on the type of gem. For example, most emeralds naturally have eye visible inclusions which do not affect the value of the gem, while most other gemstones possess no inclusions by nature.
Therefore, clarity should be evaluated on the basis of the type of color stone. A good rule of thumb is to look for a gemstone that does not have the inclusions under the table area. Make sure the gem does not have any surface reaching inclusions or chips which would affect its durability for daily wear.
Most color stones are cut to ensure the best potential color when facing up. Sometimes a cutter has to cut the pavilion to unusual proportions in order to achieve the best possible color face up. As long as the shape of the gemstone is not compromised, the actual number of facets or placement of facets will not devalue a gemstone. However, if most of the weight of the gem is found underneath the stone, this will result in a smaller looking stone face up. This gives you less value for the purchase price.
In contrast, if the cut of the gem is too shallow, you might see a window effect in the color gem. This window is an area of the gemstone where the color is less saturated. The best way to evaluate the cut of your color stone is to compare it to other gems in the same shape and weight range.