Spring
The trees get a beautiful colour, the water and sky will get a warm colour, the entire world will be flooded with flowers and baby animals can be found around every corner.
Summary
Spring starts on March 4th, see calandar system
Leaves in forests will turn pink and water will have a slight light-blue tint
The sky has a light-blue colour
Flowers can be found everywhere, the entire world will look like a flower forest
Snow and ice generated in winter will be removed
Lots of sheep, cows, pigs, rabbits and chickens will spawn each with 3-5 babies
Fireflies will spawn at night
Increased spawn rate of bee's
Length of the day and night are mostly equal, see day and night cycle.