Complex sentence: The high-energy and high-frequency light is scattered out the most and the remaining low-energy, low-frequency reaches the observer at horizon at twilight, backscattering of this light further turns it pinkish-red.
Split into simpler sentences: The high-energy and high-frequency light is scattered out the most and the remaining low-energy, low-frequency reaches the observer in the horizon at twilight. The backscattering of this light further turns it pinkish-red.