The mesosphere itself doesn't have a color. It's a layer of Earth's atmosphere, and like the other layers, it's transparent to the human eye.

However, the mesosphere can appear black at night, because there's very little light scattering happening in that layer. During the day, it can appear blue due to the scattering of sunlight by the thin air.

It's also worth noting that some atmospheric phenomena like noctilucent clouds are visible in the mesosphere. These clouds are very high-altitude and appear as shimmering, silvery-blue clouds.