I've had a few Hershey chocolate bars in the past that had a white surface coating. After a bit of searching, I found this is called bloom. I'm not sure if this is sugar bloom or fat bloom, but it was from a newly bought chocolate bar. I actually, and apparently unpopularly, enjoy this effect. Is there a way to induce it in store bought chocolate? 
Since @TBonamigo have already addressed sugar blooming, I will comment on fat blooming.  Fat blooming is the migration of fat from the bulk of the chocolate to the surface. Why and how blooming happens is not an easy question, and there is a lot of research in the industry trying to address the problem.  But we can build a heuristic picture. The first important information is that when liquid cocoa butter cools, it forms a solid crystalline structure. Different spatial arrangements of the fat molecules lead to different crystalline structures, each characterized by different physical properties such as melting point, specific heat, and resistance to strain.   If you melt your chocolate and let it cool randomly, it will (almost) randomly crystallise in these different shapes. The result is a polycrystalline solid. Since some of these crystals have a lower melting point, imagine that with temperature fluctuation some of them can melt and become a liquid trapped in the unmelted crystal. But since liquids occupy a higher volume, this generates pressure that 'push' the liquid fat to the surface. This migration also increase the porosity of the chocolate which itself helps blooming.  Chocolate makers usually want to reduce this effect by controlled cooling o form a uniform structure with the most stable crystals. If most of the crystals have the same (high) melting point you reduce blooming. This is achieved by tempering, and your industrial bar is usually in this phase.    With the science in mind, an easy way to get fat blooming is untempering your chocolate by melting it completely and let it cool into a polycrystal at room temperature. From personal experience this usually leads to blooming within a few days. If you cool in the fridge and after let it sit at room temperature It might even accelerate the process, since you are creating more drastic temperature fluctuations. 