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 AWC Pearl Gold C (15 ml) is described as a pearl-gold watercolor. Gold watercolor gives artwork a metallic, light-reflecting finish rather than the flat appearance of ordinary yellow or ochre paint.
Pearl Gold Green is a shimmering green with warm golden reflections. It belongs to Holbein's Artists' Pearl Watercolor range, which combines transparent color pigments with reflective gold or silver pigments to create a lustrous finish.