The three most widely-recognized non-diamond gemstones, sapphires, rubies, and emeralds, typically have some mineral traces or inclusions. You'll have a hard time finding rare (and very expensive) slightly-included or flawless gems. But you shouldn't worry too much; the jewelry industry considers even moderately-included gems "desirable."

• Emeralds: Emeralds range from yellow-green to blue-green. The most valuable stones are pure green. Considered the birthstone of the month of May, emeralds are also the anniversary gemstone of the 20th, 35th and 55th year of marriage. Emeralds lend themselves to elaborate carving and inscription because of their composition.
• Rubies: Traditionally considered the most valuable gemstone, rubies are the birthstone for the month of July and traditional 15th and 40th year anniversary presents. Ruby hues range between orange-red and purple-red. 
• Sapphires: Sapphires represent September birthdays a well as 5th and 45th wedding anniversaries. Hue ranges from blue-green to blue-purple, but sapphires also come in many other colors including colorless, white, yellow, orange, pink, brown, and black.

Evaluating Gemstone Color
When shopping for gemstones pay close attention to color. Unlike diamonds, different gemstones have different densities, rendering carat weight useless as an accurate measurement of size (to determine size, look at diameter, length, and width measured in millimeters). In other words, a lighter weight gem with even color may be more valuable than a heavier gem. Also, the color of good stones can mask inclusions more than in diamonds. You should look for three aspects of color:

• Hue: Hue is the unique color of the gemstone. While almost all stones have some shades of other colors, the most valuable stones present the purest hue: red rubies, green emeralds and either blue or pink sapphires.
• Tone: Tone is the depth of a gemstone color, from colorless to black. Tone is described on a scale that ranges from light to medium to dark. The most valuable stones range from medium-light to medium-dark
• Saturation: Saturation is the purity of the color throughout the gemstone. A gem that is free of gray or brown hues is said to be strongly saturated and is more valuable than a stone with lower saturation. Saturation often determines the cut of a gemstone. A high-quality gem cut delivers an even color throughout the stone and exposes the fewest inclusions.

Stones with a deep, saturated color look best and are most valuable with a shallow cut that allows consistent, bright color. A stone with less color saturation should be cut more deeply to let more light into the stone for sparkle. Symmetry (the balance of the gem's facets) and polish (the surface smoothness of a gem) also affect the sparkle of the gem and can enhance or detract from its value.

compiled in part from Ebay