TNT is poisonous and skin exposure will generally cause irritation and your skin will turn bright yellow or orange.  Further, if you eat TNT, your pee will turn red and look like blood, though it is not.

During WWI, munitions workers who handled TNT were called “canary girls” or “canaries” because their skin that was exposed to the TNT turned yellow.  Not only were they subjected to a girly nickname, but prolonged exposure to TNT causes liver, blood, spleen, and immune system problems among others.  Sort of kicking them while they are down.

Sources and Further Reading