“Humayun was matchless in the science of astronomy, astrology and other strange arts.”
In Hindu astrological traditions, planets associated with a day of the week are worshipped as deities. To seek benefit of the powers associated with the planets, Humayun matched the colour of his robes to correspond to the colour of the planet of the day. 
On Sunday, day of the Sun, for instance, the emperor wore yellow, “and like the Sun, which illuminates the world, the King sat on the throne”. Tuesday, associated with the red planet Mars, was the day for the patron of warriors, thus Humayun clad in red would dispense justice. On Saturday, which was associated with the planet Saturn, he would wear only black. Thursday was associated with Jupiter, the planet of the learned, and on this day Humayun wore beige and received virtuous men. Monday, the day of the Moon, Humayun would be dressed in white, and on Wednesday, the day of Mercury, the emperor wore purple or blue. On Friday, the day of Venus, he wore green. 
On each of these days, the Taj-i-Izzat was also worn in the appropriate single colour. This Hindustani tradition of wearing planetary colours, preceded Humayun by centuries and continues to be popular to the present day.