Blue Flame

In Ocarina of Time, Blue Fire can be found free of charge in Ice Cavern and Ganon's Castle, or for 300 Rupees at the Magic Shop in Hyrule's Market as a child or Kakariko Village as an adult for 300 Rupees. Additionally, Blue Fire can also be found in Master Quest's version of the Gerudo Training Grounds.

In any case, an Empty Bottle is needed to store Blue Fire. The only function of the uniquely-colored fire is to melt Red Ice.

The Blue Candle from The Legend of Zelda is similar in appearance to Blue Fire, but the two items are very different in function.

Speculation
When Keese fly through Blue Fire, they become Ice Keese, and when Link touches Red Ice he does not freeze like when he contacts regular ice, which gives rise to the belief that perhaps Red Ice is hot.