Color is the most significant factor affecting a ruby’s value. The finest ruby has a pure, vibrant red to slightly purplish red color. In most markets, pure red colors command the highest prices and ruby with overtones of orange and purple are less valued. The color must be neither too dark nor too light to be considered finest quality. If the color is too dark, it has a negative effect on the stone’s brightness. At the other extreme, if the color is too light, the stone may be considered to be a pink sapphire, even if color strength or intensity is high. That said, pink sapphires enjoy a following, at a far more competitive prices than rubies. Ultimately, the most desirable color of ruby is the one you prefer the most.
The Difference Between Pink Sapphire and Ruby
Some gem dealers debate the borderline between ruby and pink sapphire. Historically, the word ruby referred to shades of red, which technically included pink. There are also cultural differences in the interpretation of ruby versus pink sapphire. In some gem-producing nations such as Sri Lanka, pink colors were always considered ruby, while in many consuming countries it is classified as pink sapphire. The GIA Laboratory uses a controlled set of comparison stones called masterstones to determine if corundum is ruby The laboratory grades its masterstones on the principle that red must be the dominant hue before a stone can be called a ruby. In the gem trade, though, pinpointing the dominant hue is subject to personal perception.
Burmese Pigeon Blood Ruby
Historically, the term “pigeon’s blood” described the red to slightly purplish or pinkish red color of rubies with a soft, glowing, red fluorescence. Traditional descriptions like these are useful for evoking images and describing color among professionals. But they can be subject to misinterpretation when used to describe a ruby’s actual color. Over time and years of experience trade terms can conjure up perceptions of certain colors and qualities that are associated with a stone’s source. However, the qualities might be typical of that source or they might represent the finest stones from that source. A single source never yields gems that are all the same color and quality. In fact, the descriptive trade term might represent only a small, yet highly desired percentage of stones from that source. New sources can produce material very similar to rubies from classical localities or present a slightly different appearance, but remain just as beautiful.
Ref : https://www.gia.edu/ruby-quality-factor