The use of natural essential oils creates molecules that are captured in the fibers of the wick, kind of like water or air filters. Some of our natural elements, especially vanilla and oils derived from wood, are naturally brown or yellow in color. Wicks can have a brown or almost burned appearance as these naturally tinted molecules work their way through the fibers. Remove your refills when empty, since prolonged exposure to heat can exacerbate the discoloration of wicks. You likely will NOT notice the same phenomenon with synthetic store-bought brands, but you may notice artificial dye in their wicks. Rest assured the discoloration you may see on our wicks is naturally colored fresh content, not chemicals or dye.