The phrase "winter sky" refers to the sky during wintertime. It usually means a sky that is seen during the winter season, which can often be cold, clear, and have a unique appearance with possibly grayish or blue colors. Full definition
There is a gorgeous view out the window of a giant tree which was in full bloom that month, a magnificent contrast to the gray seaside winter sky. (boba.com)
Clean white vintage dishes and shiny antique silver would complete the color scheme reminiscent of a clear winter sky at midnight. (designsponge.com)
It's on a pier near my house and I love the color — especially when winter skies get gray. (momtrends.com)