Recently came across the phrase “Light the blue touch paper” and wondered what it meant.
If someone lights the touch paper or lights the blue touch paper, they do something which causes anger or excitement.
The basis of the phrase is in the meaning of “touch-paper”, which is a paper steeped in saltpeter, which burns slowly, and is used as a match for firing gunpowder, and the like. (http://www.thefreedictionary.com/Touch-paper). Lighting it initiates the process leading to the explosion. To "light the blue touch paper" is simply a colloquial expression meaning "to kick things off" or "to get things started"