Marlene wakes up early in the morning and her room is fairly dark. She looks over and sees her shirt hanging on a hook. She knows it's her red shirt because she hung it up there before she went to bed, but in the dark she cannot see its color. It looks dark gray to her. Why is that?

 Cones in eyes are ineffectual in dim light

Explanation:

Cones are photoreceptor cells of eye that provide different response towards varying wavelength of light .They can effectively function in bright light and provide color vision of things.They tend to become ineffective in dim light or darkness as photoreception becomes improper.

According to the question, Marlene's shirt is looking dark grey in color in darkness rather than red(actual color in brightness) because cones of eyes have become ineffective in darkness

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