Deep sky blue

Quick answer：

Deep sky blue is a color that represents the color of the clear night sky as seen from the Earth. It is a shade of blue with a hex code of #0000FF and is often used in art, design, and astronomy to represent the night sky. The color has a wavelength around 490 nm and is named after the deep blue color of the night sky, which is caused by the scattering of shorter blue wavelengths by molecules in the atmosphere.