Why can a refrigerated chocolate bar turn grainy and pale after it warms to room temperature?

Answer: Condensation dissolves surface sugar, which recrystallizes as a pale gritty layer

Condensation dissolves surface sugar, which recrystallizes as a pale gritty layer ✓ — Condensation is the cause: moisture from the air dissolves sugar at the chocolate surface. As that water evaporates, the sugar recrystallizes into a pale, gritty layer. This is why the change often appears after a cold bar warms up in a humid room.

Milk solids separate from cocoa butter and rise to the surface — Milk solids do not separate and rise to the surface when chocolate warms. Milk proteins and fats can affect texture and crystallization, but the pale gritty layer is sugar that has dissolved and recrystallized. That surface change comes from water and sugar, not from milk solids floating out.

Cold destroys cocoa flavor and leaves a dull taste — Cold does not create the pale, gritty surface; it can only mute aroma and flavor a little. A cold bar may taste flatter because its aroma compounds are less noticeable, but that is a tasting effect, not a coating. The pale layer needs water at the surface, not just low temperature.