Density variations in air caused by air being warmed by the flames of 4 candles cause light rays passing through these regions to pass through a "color filter array in a Schlieren beam in a manner unlike that which would be the case if the air above the candles were of uniform density in which case the field would simply be tinted blue. Where the gradient (change) in density is from hot to cold air it is possible that the light rays are bent towards a green filer and where the density changes from cold to hot the deviation would be towards a red filter.