Is red a royal color

There are several reasons for calling Purple a royal colour:-

Only the most expensive dyes were used to produce the color purple, it therefore became symbolic with wealth and power.

Purple togas were worn by the all powerful Roman Emperors.

People who were allowed to wear the color purple during the Elizabethan era, as decreed by the English Sumptuary Laws, were the Queen, Queen's mother, children, and sisters, and aunts. The King, King's mother, children, brethren, and uncles