Holbein AWC 15ml Pearl Gold Blue C – W815 appears to refer to a special-effect watercolor, but I couldn't verify the exact shade name and code combination in Holbein's official catalog. Holbein does make iridescent watercolors that create a shimmering, color-changing effect.
Holbein Artists' Watercolour preserves the brush handling qualities found in traditional Japanese watercolour techniques. They are produced without ox-gall, animal by-products, or other dispersing agents, allowing for greater colour density and brush control.