Grises literally translates to "grays." While it's a common color, its use in the phrase "lluvia de grises" (rain of grays) is what makes it interesting and unique in this song.
In the context of the lyrics, "lluvia de grises" is a poetic metaphor for a period of sadness, melancholy, or emotional dullness that the singer experiences after a breakup. It evokes an image of a dreary, colorless emotional landscape, making it a powerful and memorable way to describe heartbreak.
Virlan Garcia's "Lluvia De Grises" is a powerful song about the bitter aftermath of a breakup, told from the perspective of someone who was left behind. He sings about the difficulty of accepting that his ex is gone, but even harder, loving someone who didn't appreciate him. He remembers all the quality time he gave, hoping she'll realize what she lost when she doesn't have his arms to turn to anymore.
He recalls her leaving without warning, bringing a "lluvia de grises" [rain of grays] into his nights. Now, he imagines her wanting to call and beg, but he won't be there because it's too late – he's busy fixing the mess her departure left behind. The bluntness of lines like "Tú que me dijiste / Que no te importaba / Que no dolía nada" [You who told me / That it didn't matter to you / That nothing hurt] really hits hard. He points out the irony: she's now sad and crying, even though she was the one who ended things. It's a classic tale of regret, but with a satisfying twist of the tables turning.