The symbol of the Third Imperium established
by Cleon (the first emperor) when
the empire was proclaimed. Images show him
standing before the original banner with a golden yellow sunburst against
a black background, representing Capital's
type G star against dark space.
In 247, the Eliyoh (a non-human minor race) joined the Imperium. To that race
the symbology was unimpressive. The Eliyoh vision centered in the far infrared,
which resulted in distinction between the official colors of black and yellow
being impossible. So the Empress Porfiria
declared that the symbol would have no official color.
The original banner in the Imperial throne room is still black with a yellow
sunburst. The Imperial Interstellar Scout Service uses a red sunburst; the
Imperial Navy, yellow; the Imperial Army, black; the Imperial Marines, maroon.