This is the first part of the weather-lore rhyme:
Red sky at night; shepherds delight, Red sky in the morning; shepherds warning
The saying is very old and was probably passed down by mouth before being written down. There is a written version in the Wyclif Bible in 1395 and later from Shakespeare, in Venus & Adonis, 1593: "Like a red morn, that ever yet betoken'd wreck to the seaman - sorrow to shepherds."
The colour in the sky at dawn and dusk is because the sunlight has more atmosphere to go through than during daylight. The red wavelength is better reflected off of clouds than blue light which scatters before reaching the clouds. With our prevailing westerly winds, If they are there making the sky red at night hopefully by the morning they will have passed to the east giving us good weather. Well that's the theory anyway!