RFNA is a rocket fuel (a storeable oxidiser): red fuming nitric acid. HNO3 + 13% N2O4 and 3% H2O. The colour of the resulting red fuming nitric acid is imparted by N2O4, which breaks down partially to form NO2, the actual source of the color.
Usually used with an inhibitor (various, sometimes secret, substances - hydrogen flouride is one - it is then referred to as IRFNA) because HNO3 attacks most container materials.
It can also be a monopropellant; with substances like ammonium nitrates dissolved in it, it can be used as the sole fuel in a rocket. It is not normally used this way however.
More at: http://www.astronautix.com/props/nitidjpx.htm
