One F!rosh Week tradition is purple dye, where F!rosh and Leedurs alike dye their bodies (or parts thereof) purple. The colour purple represents great significance in the traditions of engineering schools across Canada. Many engineering students take the opportunity to dye themselves purple over the course of their Orientation Weeks to signify their dedication to their profession. In recent years, Skule™ engineering students have also begun to dye themselves purple prior to participation in the annual Pride Parade.
The Colour Purple
The history of the colour purple and its association with engineers has a somewhat mysterious origin, and some stories are of dubious veracity.
One verifiable fact is that the British Merchant Naval Engineers are distinguished from other types of officers by the colour purple on the piping of the officer's braid, a feature still common on certain uniforms today.
It is also said that the Royal Military Corps of Engineers wore purple arm bands to distinguish themselves as members of their profession. Their sweat and the brine from their working conditions caused the dye from the arm bands to seep into their skin, dyeing a patch of skin purple. These engineers were highly respected and celebrated as people of personal sacrifice, always ensuring that they did whatever what was in their power to repair damage endured by ships, allowing passengers more time to escape to safety. Engrossed in their life-saving efforts, the engineering often made the ultimate sacrifice, and slipped into the depths along with the failing ships.
Another commonly attributed story is linked to the purple background on the insignia of rank worn by British Marine Engineer officers. Around 1865, British naval engineers wore purple backgrounds on their rank insignia to distinguish them from other officers, and that became common among British mercantile engineer officers when they started wearing uniforms. It is said that these officers, distinguished by their purple insignia were aboard the Titanic and remained on board to delay the ship's sinking. One variation of this story holds that the purple was actually bestowed by King George V on the engineering corps after their sacrifice and heroism in the engine room of the Titanic, although this story is almost certainly mythical. 
History at Engineering Schools
The actual tradition of engineering students dyeing themselves purple appears to have begun around the late 1970s and early 1980s. The tradition is said to have started at Queen's University or Western University, whom had used certain purple colouring on their bodies to symbolize the profession of engineering. This practice gradually turned into a full-body dye for many.
The purple dye usually found during orientation week is made with gentian violet (also known as crystal violet or methyl violet 10B), a synthetic chemical which has a long and varied history as both a medicinal agent (as an anti-bacterial and anti-fungal agent) and as a dye. The synthesis of gentian violet has been attributed to French chemist Charles Lauth as early as 1861, originally named "Violet de Paris". It has also been used to dye paper, as a component of navy blue and black inks, and as a colourizer for certain household products.
To create the dye for orientation week, a mixture is created consisting of isopropyl (rubbing) alcohol, water, and gentian violet stirred in a large drum. The alcohol acts as a useful solvent to ensure that the dye will dry more quickly, as well as maintaining the solution’s sterility. The amount of water in the dye determines its strength, and therefore how easy or hard it is to remove it. The less water added to the mixture, the longer it will stay on the skin. The dye used for F!rosh Week is usually composed of one gram of dye per 600 litres of water. At this strength, it tends to come off in a day or two with vigorous scrubbing. However, the nails and hair will remain purple longest, as those cells are very slowly replaced.<ref>Michael Au, "The Science Behind Purple Dye", The Cannon. http://cannon.skule.ca/the-science-behind-purple-dye-3/</ref.