Color is the single most important quality factor for colored gemstones. It can account for 50-70% of a stone's value. Unlike diamonds — where the absence of color is prized — colored gemstones are valued for the richness, purity, and beauty of their color.
Gemstone color is evaluated across three dimensions: hue, tone, and saturation.
The Three Dimensions of Color
1. Hue — What Color Is It?
Hue is the dominant spectral color — blue, red, green, yellow, purple, orange, or pink. Most gemstones also show secondary hues. For example, a sapphire might be described as "violetish blue" (blue is the primary hue with a violet secondary) or "greenish blue" (blue with green).
Generally, the purer the primary hue — with minimal secondary color — the more valuable the stone. However, some secondary hues are desirable: a slight violet in a sapphire can enhance its appearance, while green in a sapphire diminishes it.
2. Tone — How Light or Dark?
Tone measures how light or dark the color appears, on a scale from "very light" to "very dark." The most desirable tone varies by gem type:
- Too light: The color appears washed out or pale. The stone may look like a lighter, less valuable variety.
- Medium to medium-dark: Generally the sweet spot. The color is rich and vivid without losing transparency.
- Too dark: The stone appears almost black. Even if the body color is fine, an overly dark tone makes the stone look inky and lifeless.
3. Saturation — How Vivid?
Saturation describes the intensity or purity of the color — how vivid it is versus how grayish or brownish it appears. Saturation is often the key differentiator between a $500 sapphire and a $5,000 sapphire of similar size.
- Strong to vivid saturation: Pure, intense color with no gray or brown modifiers. Commands the highest prices.
- Moderate saturation: Attractive color but with some grayish or brownish quality. Good value.
- Weak saturation: Grayish or brownish overall. May look dull or muddy.
Premium Colors by Gemstone
| Gemstone | Premium Color | Description |
|---|
| Ruby | "Pigeon Blood" Red | Vivid, slightly purplish red with strong saturation. Medium to medium-dark tone. The most valued ruby color, historically associated with Burmese stones. |
| Blue Sapphire | "Cornflower" or "Royal" Blue | Vivid, medium-toned blue with velvety saturation. Not too dark, not too light. Kashmir and Ceylon sapphires often show this quality. |
| Emerald | "Muzo Green" | Vivid, slightly bluish green with warm undertones. Medium tone. Named after Colombia's legendary Muzo mine. |
| Tanzanite | Vivid Violet-Blue | Intense, saturated blue-violet. Stones that show strong blue and violet pleochroism are most desirable. |
| Aquamarine | Medium Blue | Clean, medium-toned blue without green modifiers. Saturated aquamarines over 5 carats are premium. |
| Pink Sapphire | Vivid Hot Pink | Intense, saturated pink without gray or brown. Medium tone. Borders on "ruby" in the reddest examples. |
| Morganite | Peach to Salmon Pink | Warm, peachy pink with moderate saturation. Larger stones (3ct+) show the best color. |
| Tourmaline | Varies by color | Paraiba tourmaline (neon blue-green) is the most valuable. Chrome green and rubellite (red) are also premium colors. |
Special Color Phenomena
- Padparadscha Sapphire: An extremely rare pinkish-orange sapphire named after the lotus flower. One of the most valuable sapphire colors, with fine examples exceeding $30,000 per carat.
- Color Change: Some gems (alexandrite, certain sapphires, garnets) shift color under different light sources — green in daylight, red under incandescent light. Strong, distinct color change is highly prized.
- Bi-Color / Parti-Color: Tourmaline and ametrine can show two or more distinct colors within a single stone. Valued as novelties, especially when the color zones are well-defined.
- Star Effect (Asterism): Rubies and sapphires sometimes display a 6-rayed star when cut as cabochons. The star should be centered, sharp, and visible against a richly colored body.
Why Labs Don't Give Color Letter Grades
Unlike diamond color (D-Z), gemstone color is not assigned a letter grade on lab reports. Instead, labs describe the color in words — for example, a GIA report might say "Blue" or "Vivid Blue" while a GRS report might use their proprietary descriptors like "Royal Blue" or "Pigeon Blood." This is because colored gemstone color is far more complex than diamond color and does not fit neatly into a linear scale.
This means you must evaluate color yourself — through high-quality photography, 360° video, or ideally in person. A stone described as "Blue" on a lab report could be a pale grayish blue or a magnificent vivid blue — the report alone won't tell you which.