Blue could also mean dark green, violet, black or brown. The ancient Greek word for a light blue, "glaukos", also could mean light green, grey, or yellow. The Greeks imported indigo dye from India, calling it indikon. They used Egyptian blue in the wall paintings of Knossos, in Crete, (2100 BC). It was not one of the four primary colours for Greek painting described by Pliny the Elder (red, yellow, black, and white), but nonetheless it was used as a background colour behind the friezes on Greek temples and to colour the beards of Greek statues. The Romans also imported indigo
Road signs in the United Kingdom patch may only be coloured blue or green. Signs indicating a temporary change, such as roadworks or route diversions, are denoted with a yellow background. Usually these signs use a simple black on yellow colour code, more complex signage use the conventional signs superimposed onto a yellow background. In some areas, such as the Dartmoor National Park, additional signs and colours are used to distinguish road conditions. In addition to the national colour schemes, the park also uses white signs with a light blue border and text to denote routes suitable for medium-sized vehicles and white signs with a brown