Why are diamonds more popular than colored gemstones?

Many reasons, here are some..

• Marketing: You’ve probably heard of the most successful marketing campaign in the history of mankind: De Beers ‘A Diamond is forever’ slogan. Apart of Tanzanite (marketed by Tiffany & Co.) and couple other gemstones, colored gemstones never had the chance to be featured under the spotlight as extensively as diamonds were. Although both may reach prices higher than diamond, few people will recognize what a ‘Color Change Chrysoberyl’ is, fewer will know what a ‘Paraiba Tourmaline’ is, but it’ll take a caveman not to know what a diamond is.
• Pricing & Transparency: While the transparency of diamond pricing -guided by major miners such as ALROSA & De Beers, and released monthly/weekly on a subscription list by the Martin Rapaport Group- isn’t even close to that of gold and precious metals, it still exist at the very least. In the colored gemstones market none of that exists, probably no other market has the level of freedom and openness colored gemstones market has. This fact -with other facts I’ll mention later- makes it impossible to put a practically useful pricing list or guideline for colored gemstones, which translates into more buyer hesitation and mystery surrounding this section.
• The very unique nature of diamonds: ‘simplicity is the ultimate sophistication’, and in the world of gems and crystals, it doesn’t get anymore simpler than ‘C’, pure Carbon. The simple composition and unique chemical and physical properties of diamonds naturally sets it apart of other gemstones, somewhat validating an economical separation.
• Markets maturity & the way people understand luxury: We tend to think of diamonds as a luxury product, which is theoretically true. But take a look at women’s hands in your city next time you use the metro or public transportation, no matter big or small, you’ll probably see diamonds on most fingers, and definitely on a married woman’s finger, making it practically so mainstream and, dare I say, not that rare. On the other hand, when was the last time you saw a woman with a Ruby or Emerald ring? For this reason, when analysing the level of maturity of a certain luxury market experts take note of how attracted their women and general population are to gemstones like Ruby, Sapphire, Emerald and even pearls, rather than diamonds. As such gemstones mark the fine line that sets dominantly commercial markets (Ex: Middle-East..) where women mostly care about what the media and marketing machine lead them to believe, sets them apart from mature ‘high-end’ markets (Ex: Hong Kong, Japan..) where women are inherently cultured to understand luxury and make purchase decisions based on their own preferences and understanding of the historical and artistic value of the material. For this reason as well, when you open a Christie's catalog on the jewellery section, you’ll see pages dominated with colored gemstones minimally accented with diamonds. Diamonds are for the mainstream and middle-class, precious colored gemstones are for royalties and upper-class, so it makes sense for diamonds to be more popular as the middle-class makes the majority of societies.
• Gemological Laboratories Standards & Terminologies: Most renown gemological institutes and laboratories (GIA, HRD, Gübelin, IGI, Etc.,) agrees on what a VVS1 clarity F Color diamond is, there’s a universal standard for this. But due to their complex physical and chemical nature, there’s no such consensus or agreement over colored gemstones. You might send a Ruby to laboratory X and get a ‘Ruby’ identification in their report, send the same Ruby to laboratory Y and get the most sought-after ‘Pigeon-Blood Ruby’ identification in their report, the result difference might seem simple, just two extra letters right? But it’s problematic as these two letters translates into hundreds of thousands of dollars difference in price point. The same applies to origin reports, where we use trace elements and certain inclusions in a gemstone to locate the geographical origin and the result isn’t always 100% accurate, as some of the machines analysing this (check Origin determination techniques) are sensitive and prone to the environment. I have seen conflicting origin reports for Emeralds where reported Colombian origin was actually Brazilian, and vice-versa. While rare, these faulty identifications are very problematic and harmful to the colored gemstones industry, it also translates into more buyer hesitation.

Take this for example, the famous Sunrise Ruby, this was sold for a whooping 30 Million dollars in a Sotheby's auction in Geneva 2015. If it wasn’t described as ‘Pigeon-Blood Ruby’ by reputable gemological labs, we’ll never hear of it next to such number.

• Manufacturing & Calibration: Colored gemstones jewellery is harder to make and requires special care throughout manufacturing, as -depending on the type of gemstone- it might react badly to some of the processing stages like a torch’s heat, Electroplating and ultrasonic or steam cleaning. While diamond jewellery withstands a certain amount of heat and doesn’t react neither to plating nor to ultrasonic & steam cleaning. Also, diamonds are more readily available in regular ‘calibrated’ sizes than gemstones are. These two reasons leads to more diamond jewellery being made than colored stones jewellery, as most manufactures want to save themselves the troubles that comes with colors.
• Variety of groups, species, varieties and treatments: The listing of nature’s menu when it comes to gemstone species is long (List of gemstone species), so long that it became a branch of science on its own called ‘Gemology’, many of these species branch out to varieties, and each variety might have its own origins, color range and treatments, each variable affecting price and demand. While a diamond is a diamond, it might have a tint of color, might have some cute inclusions, maybe some laser drilling or irradiation treatment, but that’s about it. Simpler to understand, thus simpler to sell.

So there you go, these are some of the reasons that comes to my mind on why diamonds are more popular than colored gemstones.