Ruby is one of the highest valued coloured gemstones, in fact, large rubies can fetch higher prices than equivalently sized diamonds. The colour of ruby is its most important quality factor. The most sought after colour is a strong pure red to red with a hint of blue. This vibrant red hue is known as "pigeon's blood". When the colour of ruby is too light, it is classified as pink sapphire, but the line between pinkish-red ruby and pink sapphire varies by region. Some mining areas consider pink ruby to be ruby.
Ruby typically displays inclusions and these are tolerated as part of the nature of the stone. However, when inclusions minimize transparency or brilliance, they decrease the value. Ruby that is free from eye visible inclusions is available, however, large eye clean gemstones are rare and extremely valuable.