Jerry prefers to burn bituminous coal in his fireplace because of the yellow flame. what causes that flame color?

Bitumionous coal burns with yellow flame because of the incomplete combustion of the hydrocarbons in it. The color of flame indicate the combustion of the hydrocarbon contain of the substance. Normally a blue flame indicate complete combustion of the substance releasing carbon dioxide.
However in case of incomplete combustion, which happen due to poor supply of oxygen, causes yellow flame and shoot. In incomplete combustion, carbon monoxide and carbon are released.

Also due to different impurities contained in Bituminous coal,like sulfur, it burns with yellow flame.