alexandrite is the highly regarded color changing variety of chrysoberyl. the color of alexandrite changes under different lighting conditions. if viewed in daylight, its color is greenish blue to dark yellow-green.
emerald is a gemstone and a type of the mineral beryl colored green by trace amounts of chromium and sometimes vanadium. emerald in antiquity were mined in Egypt at locations on Mount Smaragdus since 1500 BCE.
yellow sapphire is a gem of the corundum family and is a twin of ruby and blue sapphire. it is available in yellow, golden and orange colors. the highest quality is known to be of lemon-yellow color. the color in yellow sapphire is of iron and titanium.