I guess the only time for sapphires to turn rainbow is when the light catches on their individual facets, separating white light into their many different composite colours, much like how diamonds and their facets do. When I was younger I might have wondered why diamonds are so commonplace in jewelry but not sapphires. As a kid, blue used to be my favourite colour, especially of the bright blue variety. But I guess sapphires being blue has its own personality and association. Blue can be associated with calmness, sadness, even royalty, I guess? That could be how we have our phrase ‘royal blue’. Diamonds on the other hand, looks colourless, yet very shiny, so I could see how they have universal appeal. Colourless things are like canvases in one aspect; they can be made into any theme, mood or design whatever one likes. I suppose using sapphires for an engagement ring or wedding band must be quite difficult. Imagine a band of small sapphires surrounding a larger, pronnged sapphire in the middle. It doesn’t shine that much with its colour covering it, so it kind of defeats people showing off their hand and proclaiming, “I’m engaged/married!”
Just like canvases, diamonds are malleable in their design and can be used across all kinds of jewelry. So even with the controversy surrounding ‘blood diamonds’ diamonds will inevitably still be utilized for their design versatility.