Three different alignments were the original ones: white, red and black. The wizards following Solinari wear white robes of good, the ones following Lunitari wear red robes of neutrality, and wizards following Nuitari wear black robes of evil.
Tracy Hickman defines the color of the robes as something beyond simply alignment:
|color:#B2B7F2;font-size:35px;font-family: 'Times New Roman', serif; font-weight: bold; text-align: left; padding: 10px 10px;">“||The color of a mage's robe on Krynn are more than just an ornamentation or sign of fealty to a particular order of magic. The color of a mage's robes reflects an entire attitude and philosophy of magic — a magical way of life, if you will.||”|
The Knights of Takhisis recruited renegade mages. These wear grey robes, and are despised by the original Orders as they work for the grandness of Takhisis instead of the Children of magic. For other renegades, the robe color means nothing, and they can be found wearing red, white, black or any other color. Mages who left the Order to practice magic before their Test, but are not renagades, wear brown robes. This was shown in Brothers in Arms: Raistlin Chronicles vol. II. .
Mages are able to change their alignment, although the price is usually high.
Read more about this topic: Wizards Of High Sorcery