The colored condensates bursting in your flame are some of the hazardous chemicals in your gas. And those non-methane combustion byproducts coming from the gas company are entering the indoor air. Natural gas indoor environmental smoke test. Remove wall pictures and hangings, looking for a shadow behind where the object hung. The shadow is cleaner than the surrounding surface because combustion from gas appliance flames deposits environmental smoke covering everything indoors.
Objects hanging on the wall collect the gas smoke and shield the wall.
Look at the bottom of your pots and pans used on gas appliances. See those dark sooty smudges, that's environmental smoke etched into the metal. These chemicals are so powerful, they eat into the metal surface and can't be removed. Think what they are doing to your lungs. If you have a fireplace with a gas log insert, look at the black sooty deposits coating the hard ceramic.