"Mother of Pearl" clouds over Oslo in 2014! I have never seen so beautiful clouds before! Nacreous clouds, sometimes called mother-of-pearl clouds, are rare but once seen are never forgotten. They blaze unbelievably bright with vivid and slowly shifting iridescent colours. They are seen mostly during winter at high latitudes like Scandinavia, Iceland, Alaska and Northern Canada. Nacreous clouds far outshine and have much more vivid colours than ordinary iridescent clouds.