The colour of the shadow of an object depends on the colour of the light that is being blocked to create the shadow. If the light is white (which contains all colors), then the shadow will appear black or dark grey as the object is blocking the light. This is because shadows are the absence of light. However, if the light shining on the object is of a certain colour, the shadow may appear in a different color. For example, if a red light is shining on the object, the shadow might appear to have a slightly greenish tint because red light can stimulate the sensors in our eyes that also respond to green. But in most common circumstances, shadows will appear black or dark grey.
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