Here's why:
* The color of a flame is determined by the temperature of the burning material and the elements present.
* Hydrogen burns very hot, but it's a very simple element. It doesn't emit much visible light on its own.
* The blue color we see is actually from the excitation of nitrogen in the air. Nitrogen molecules absorb energy from the heat of the flame and release it as blue light.
Reddish-orange flames are typically associated with materials that contain carbon, like wood or propane.
