"Touch paper" is paper impregnated with saltpetre (potassium or sodium nitrate, which is used as a fuse for explosives, especially fireworks. It is usually coloured blue. Once lit it is very hard to put out. Lighting it initiates the process leading to the ignition of the firework. To "light the blue touch paper" is a colloquial expression meaning to irrevocably initiate a process or chain of events. The expression is derived from the instructions printed on fireworks, and is sometimes seen as "Light the blue touch paper and stand back". The idea is that one does a small thing (light the touch paper) and then one takes no further active part in a chain of events leading rapidly to a spectacular outcome.
Igniter cord is used with more powerful explosives found in civil engineering, mining, warfare etc.