Combustion plays a big role on the color of ash, and it could explain why your ash is burning white or dark. Research shows that when combustion takes place at a high temperature, organic material is burnt properly leading to a low concentration of nitrogen, and by extension, clear ash colors. On the other hand, when combustion occurs at a low temperature, organic compounds are not properly burnt, thereby leaving darker ash color. This shows that the color of ash, is not an indication of the quality of marijuana, rather the temperature of combustion.