According to a science experiment on ActivityTV, food coloring has the same density as water (you can watch the video here: http://www.activitytv.com/115-double-density ). And according to Physlink.com, the density of water is one gram per milliliter. So the density of food coloring must be one gram per milliliter. The University of Illinois sort of confirms this by saying when food coloring is dissolved in water, the total density will be close to that of water. For more information about how density changes with temperature and pressure check out the sources below. Hope this helps!