The orange from hypergolic propellants is the oxidizer (nitrogen dioxide from the dinitrogen tetroxide disassociating at atmospheric pressure and temperature),

The orange from hypergolic propellants is the oxidizer (nitrogen dioxide from the dinitrogen tetroxide disassociating at atmospheric pressure and temperature), not the fuel (typically hydrazine/UDMH these days, formerly analine was popular, many other fuels are hypergolic with N02/N204). If the reports are correct that the explosion is 2,750 tons of ammonium nitrate, the orange is probably nitrogen dioxide. A high concentration of nitrogen dioxide indicates that the explosion was very oxygen-rich, likely pointing to it being accidental. Ammonium nitrate is normally very very stable. Even mixed optimally with fuel oil, ammonium nitrate prills (pellets) won't reliably detonate with a No. 8 blasting cap, and in mining a small "booster" charge of TNT is used to get the ANFO going. However, very large piles of ammonium nitrate have caught fire and exploded, such as the Texas City disaster where a tanker full of ammonium nitrate burned for a long time, and then levelled a good portion of the town when it exploded.