This subject was better explained by Kantopia’s blog post about Three Houses’ Japanese title, so I will keep this brief.
The Japanese title for Three Houses is
風花雪月, which translates to Wind, Flower, Snow, Moon. It is in fact a reference to a Chinese poem by Bai Juyi, in which one of the lines says
雪月花の時 最も君を憶う
(At the time of snow, moon and flowers, I think of you.)
Snow represents winter; moon, autumn; and flowers, spring. (Wind represents summer, but it’s usually left out of the Snow Moon Flowers theme which was popular in Japan during the late Edo period).
The seasons are also tied to color combinations:
blue-white for winter, yellow-white for autumn, and pink-white for spring. Hence the color schemes for Dimitri, Claude, and Edelgard respectively.
Whether summer will come into play in the story has yet to be seen. Considering we have yet to see the “Wind” in the Japanese title, and the English tile gives prominence to the Three Houses, it seems like it will.