A sunset turns red because its light takes a longer path through the air
When the Sun is low, its light travels through more atmosphere before reaching the ground. Much of the blue and violet light is scattered away along that long path, leaving more red, orange, and yellow light to reach our eyes.
At noon the light takes the short route. At sunset it takes the scenic route and arrives orange.
Source · NOAA National Environmental Satellite, Data, and Information Service ↗