It is impossible to give a full explanation of color "seasons" here so please read the article Color Seasons. The following are brief summaries of the differences between each color "season".
Think pastel when you think spring. Although not all spring colors are pastels and not all pastels are spring colors, the frequency of spring colors matching pastel colors is quite large. Spring colors are the lightest colors of all the seasons and are also typically the most silvery or coolest in appearance. Because spring colors are typically mixed with white or silver, they tend to be muted colors.
Think pure when you think summer. The pure golden sun shining down on a pure blue ocean near a pure sandy beach lined by pure green foliage. The light is so bright and pure that every color has a high contrast to every other color. Summer colors are the purest colors. They tend to also be light, golden and warm as well.
Think of falling leaves when you think of autumn. All the pure colors of summer have begun to turn brown or orange but all the colors are not pure brown. The colors are somewhere between the vivid summer and the soft earth. Another way you can think of autumn is to think earth tones. The majority of the autumn colors are earth tone shades of brown and orange. There are shades of blue, green and purple that are autumn colors but these are blues, greens and purples that are earth tones and mixed with a small amount of brown. Autumn colors are the most muted (most mixed) and the warmest (most golden) colors. They are often dark as well.
Winter colors are the most difficult to describe. Most neutrals especially the purest grays and silvers are winter colors but then there are some very bright and vivid reds and greens that are winter colors. Winter colors are the darkest colors of all the seasons. They also tend to be very pure colors although the purest winter colors are the purest neutral grays and silvers. Winter colors tend to be pure and silvery but then again, there are shades of gold that are winter colors and the winter reds and greens are almost but not quite warm.