Do you know which colour is not used in any flag in the world? Purple is the colour which is not used by any nation in the world.
The reason for not using this beautiful colour was the method of extracting purple colour. Prior to 19th century the only way to get purple colour was from a species of sea snail. The process was so difficult that during those days purple colour was worth more than gold.
That’s why it was used only my monarchs, British royal family still values purple colour and similarly the Roman Empire used it to reflect its power and wealth.
Flags were meant to be used in large numbers and no country was willing to spend nation’s wealth of extracting purple colour so they simply avoided using this colour.
Purple lost its value after a British student William Henry Perkin found the alternate way to make purple colour. His synthetic dye colour made it possible to produce the dye with minimum cost.
But there are some flags which uses purple colour in some way such as Dominica. In which a Sisserou Parrot of Green and Purple colour can be seen.
Similarly Nicaragua flag contains a small triangle in which purple colour is used in ray of rainbow, but it is very difficult to notice it.