Obviously the most important factor for determining the worth of a colored gemstone is color.

Some types are pricier because they are rare and their color-type is so exceptional, and for the most part the finer the color the less emphasis is put on clarity, weight and the quality of cutting techniques applied. However, color is a very tricky term and the multitude of variations can perplex even the most studious amateur gemologist. Therefore the most basic parameter for evaluating color in a colored gem is purity- if the gemstone is red, is should be the most absolute hue of red; as close to the primary red of the color spectrum as possible. Certainly there are expensive, gorgeous gems of medium colors that have enormous market value, but within a gem-type category there are always the best and worst extremes.

The first thing you should realize is that without proper lighting, you will never be able to determine the true color of any gem. Artists and photographers will certainly know how important this is, as color is basically the direst result of light, and any variation in this will have a lot of impact on what you see. Incandescent light , also referred to as ‘warm light'- [the pure yellow light that comes from candles, lamps, crystal reflections and such] normally brings out the best of most gem-types. It naturally brings out the deepest hues within the gem and helps it sparkle. Fluorescent light - ‘cold light'- on the other hand, has far less real yellow in it and reflects red rays very weakly. Consequently, fluorescent light will warp the basic hue to some degree, and the gem will look less attractive.

Light is reflected differently in each stone; when light travels through the gem easily, enabling you to see through it, it is called ‘ transparent' , when the gem swallows all the light around it and reflects nothing back it is called ‘ opaque' . Lastly, when the gem is reasonably transparent, but it doesn't reflect light cleanly, it is termed ‘ translucent' . Translucence, as it pertains to gems, occurs as a diffusion of light, making the gemstone seem frosted or murky. So, there are many things to keep in mind when looking at gems. For this reason it is recommended that you don't trust your eyesight in this, however well you see in broad daylight, and make sure you examine the gemstone in proper lighting before purchase.

Some gems are so reactive to different kinds of light that they are called “color-change gems”, and they can change utterly from on color to another. Alexandrite, for example, is a green-blue gemstone by daylight and a deep purple and red shade by incandescent light. It will always display this quality and is evaluated on this sole parameter. Other gem-types will display this far less frequently, such as a few types of sapphire or garnet.