The blue whale is a dark blue-gray. Some of the skin, particularly on the back is quite blotched and mottled. When the blue whale has been in polar waters for some time, small creatures called [G 10 / diatoms] grow on its skin, giving it a yellowish color. It is sometimes known as the 'sulfur bottom' because of this yellowish coloring.
On a clear day, when the sun is shining and the sky is blue, the blue whale is able to reflect the blue of the sea and sky. This is because of the patterns of the [G 24 / pigment] in its skin. The mottled shades of its back easily absorb light, reflecting the colors around them.
Whale experts can identify individual whales by the patterns on their backs. As the sun sets and the light fades, the blue whale's colors turn from blue to an ochre-yellow color, and then to orange and red, reflecting the sun's dying light. As the sun sinks below the horizon and night falls, so the blue whale reflects the purple-blue light around it, and it finally appears black.
