It is impossible to give a full explanation of color "seasons" here so please read the article Color Seasons.
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.