Symbolism, Imagery, Allegory
"Roses are red, violets are blue, sugar is sweet, and so are you."
Or, in the case of Meursault: "The sky is green, anger is red, the sun is hot, and some poor Arab guy is dead."
Meursault devotes significant attention to the different colors of the sky, the sun's rays at different times of the day, the beach, the ocean, etc. In this book, green is usually associated with happy moments, which we know from the vague and undecipherable line: "The sky was green; I felt good." Red colors are associated with anger (like the Arab on the beach scene) or sex (like Marie's dress). It's probably no coincidence that these two are linked (as they are with Raymond and his ex-mistress).