夏色 is literally summer-like color, but it has a poetic nuance. Actually, there isn't such a color. But we sometimes use this word. When I hear "夏色", I can imagine not only the color such a blue and white, but also the color of the sea, shining sun and so on that we see in summer. 桜色 is a bit different from 夏色. It is an existing color for real. There are many words to express colors in Japan. They are almost named after nature: trees, flowers, fruits, animals and so on. Those names of colors are beautiful and impressive, I think. Honestly, I don't know all of names though xD. Please access the following URL. http://www.colordic.org/w/

夏色 is summer colors such as blue, navy blue, and white. 桜色 is the color of sakura blossom. Maybe pale pink in English. http://www.colordic.org/colorsample/2281.html