Answer: The original colour of grass is green because of photosynthesis. But in terms of reflection, it looks green because the sunlight reflects the green colour off the grass, so we see it as green.
Explanation: Sun appears white, but it is made up of the colors: red, orange, yellow, green, blue, indigo, and violet. When white light hits an object, it absorbs some colors and reflect the others. Grass appears green because it absorbs all the wavelengths except green. Green is reflected off the grass, so we see grass as green. The moon doesn’t have light of its own, the moon lights up because of the sun. So at night, as the light of the sun doesn't reach the grass directly because of the moon, it doesnt reflect any color off the grass, and so our eyes detect grass as black.
