turkey gravy when undisturbed

TURKEY GRAVY WHEN IT SITS UNDISTURBED FOR HOURS IN A CLEAR JAR, A DARK LAYER DIVELOPES UP AT THE TOP.(NO FAT) I KNOW JELITON COMES FROM THE TURKEY BONES, BUT WHAT IS THE PROPER NAME FOR THIS DARK LAYER. I KNOW IT`S THE FLAVOUR LAYER, CARMEN Toronto Canada