This is the exhaust nozzle and bell of the rocket engine. The discoloration is probably from a test burn when it was mounted on a stand. The coolant to prevent the nozzle from melting is actually the rocket fuel itself, circulated around the bell itself to pre-heat the fuel before it gets to the mixing/combustion chamber where it ignites.
VERY toxic fuel. The fuel handlers wore completely-sealed rubber suits when fueling operations were under-way and the suits were then immediately flown to Davis-Monthan AFB where they were pressure-tested for leaks and repaired if need be.