When gem-quality corundum is red, it is classified as Ruby. All other colors (pink, yellow, green, etc.) are called "fancy sapphires." The term "sapphire" alone always refers specifically to the blue variety. Color is the single most critical factor in determining a blue sapphire’s quality and value. When gemologists grade color, they look at three components: Tone ranges from light to very dark (almost navy blue-black). The most valuable sapphires fall in the medium to medium-dark range. If the tone is too light, it is a fancy light blue; if it is too dark This measures how rich and "pure" the color is. The highest value is assigned to stones with **vivid to strong** saturation. Sapphires, like rubies, usually contain some inclusions. While a high clarity is always preferred, eye-cleanliness (no inclusions visible to the naked eye) is the practical standard for high-quality sapphires. Heavily included gems can look dull or opaque. Most natural sapphires (over 95% of the market) are treated to improve their color and clarity. Treatments must always be disclosed.