Why is spring among swallows blue?

The tender blue spring not only shows the vitality of spring, but also expresses that the scope of swallows’ activities is the blue sky.

Spring is the first season of the four seasons. It is the season of recovery of all things, so "tender" means "new" and green, and "blue" refers to the blue sky. At the same time, it is stated that the range of swallows' activities is the blue sky

Swallows are the collective name for 74 species of birds in the order Passeriforme and family Swallowidae. It is small in shape, with narrow wing tips, a concave tail and short beak, weak and small feet, and not too many feathers. Swallows are one of the most flexible passerines. They mainly feed on insects such as mosquitoes and flies. They are well-known as beneficial birds. They build nests in tree holes or crevices, or drill holes on the beach, or stick mud to walls or protrusions of corridors, roofs, eaves, etc. in urban and rural areas to make nests. 3 to 7 eggs are laid each time.