Answer: 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