The bluish color of lead is due to the formation of a thin lead oxide layer on the surface of the lead. The color itself is dependent upon the thickness of the oxide layer. The thicker the layer, the darker the color until it becomes so dark that it really takes on a gray/black coloring. If you take your lead sheet or lead ingot and place it in a warm oven, the heat will accelerate the oxidation and cause a wide array of colors to appear on your lead.