Yes, yellow & darker colored FO's will turn color over time and exposed to light. Also vanillla scents will turn color over time. You may have to leave them un-scented but thay may still turn, over time, if they are on top of colored wax. My icing on brown cakes turn yellow to brown, over time. I think it has something to do with the brown color migrating into the white, over time. I wish I could keep my white, white, over time. I have tried additived & UV additive with no luck.