Ruby is actually red corundum, drawing its color from the presence of a trace element called Chromium. A few parts-per-million is enough to interact with the gemstone's chemistry to produce the red color widely coveted in the fine jewelry trade. Meanwhile, trace elements like iron and titanium can be responsible for producing a violetish-blue color, which results in the corundum specimen being designated to the blue sapphire variety.
Ruby and sapphire have very similar chemistry, with minuscule differences in the trace elements that create their differences in color. Sapphire though, is not always blue. While its bluish variety is indeed the most popular, sapphires can also come yellow, pink, green, purple, black, colorless and many other hues of the rainbow. Some of these hues may commonly occur in higher saturations than others. For example, violet-purple and green colored sapphires can appear grayish or muted in intensity, at least when compared to other gemstones of similar color (such as amethyst or emerald). All color of sapphire other than blue are grouped up and called 'fancy colored sapphires'.
The global gem market for sapphires is very diverse today. The biggest or most popular demand surges usually target blue sapphires, Padparadscha sapphires (pinkish-orange) and pink sapphires. Vivid yellowish sapphires are also commonly used, especially in seasonal tandem with the trendy color palettes governed by the fashion industry. Colorless sapphires (especially the lab-grown or synthetic versions) are sometimes utilised as diamond imitations as well, although their dispersion and brilliance are noticeably different from those of diamond.
Many sapphire colors are also produced by heating, or other more complicated enhancement procedures- like diffusing beryllium as a coloring agent into the stone's crystal lattice.
Also do keep in mind that synthetic corundum (lab-grown ruby and lab-grown sapphire) is a very common sight in today's jewelry marketplace. The flame-fusion process of creating man-made sapphire / synthetic sapphire is very widespread across many international manufacturers. Synthetic product can be created and sold at very low prices, as the creation technology (pioneered in the late 1800's) has grown accessible and affordable for many mid-scale entrepreneurs to get into.
Other similar creation methods, like the Czochralski process of growing crystal, are also being used today- not solely just for the jewelry industry, but also for military and industrial purposes as well. This is mainly due to corundum's high hardness (9) and general durability, as well as some of its other properties.
