Meths is just ethanol (Whats in beer etc) with a dash of methanol. This is done so that it is not taxed by customs. As its not fit for consumption. (methanol makes you go blind)
The also add vomiting agents so that if you drink it you will be sick, thus protecting you as ethanol is very dangerous at high %.
It can me colourless, they call that IMS. (Industrial methylated spirits)
The purple is version is normally what you find in the shops. It just dyed for saftey and to put you off drinking it.
The clear meths burns cleaner and you dont seem to get as much soot on your pans.