Ruby and sapphire are two of the most valuable and sought-after gemstones in the world. They are both varieties of the mineral corundum, and are distinguished by their color. Ruby is a deep RED hue, while sapphire is a deep BLUE. Both gems are highly durable and have been used in jewelry for centuries. The term 'HUES' is an acronym for the colors of these two gemstones: 'H' for 'RED' (ruby) and 'UES' for 'BLUE' (sapphire).