This beautiful phrase literally means "blue like the color of the sea" and is the title of this iconic song by Tim Maia.
More than just a color, it represents a feeling of ultimate peace and hope. Tim Maia sings about having "um sonho todo azul, azul da cor do mar" (a dream all blue, blue like the color of the sea) as the reason to live, even when life is hard. It's a perfect example of the poetic, soulful imagery found in classic Brazilian music.
Tim Maia starts this song with a big announcement: "Se o mundo inteiro me pudesse ouvir / Tenho muito pra contar" (If the whole world could hear me / I have a lot to tell). What he's learned is a pretty tough pill to swallow. He says that in life, "um nasce pra sofrer / Enquanto o outro ri" (one is born to suffer / while the other laughs). It's a very direct and honest look at the unfairness of the world.
But this isn't a song about giving up. It's about what comes next. Maia argues that even if you're the one who is suffering, you have a responsibility to "procurar / Pelo menos vir achar / Razão para viver" (look for / at least find / a reason to live). For him, that reason is a dream. Not just any dream, but "um sonho todo azul / Azul da cor do mar" (a dream all blue / blue like the color of the sea). This beautiful, peaceful image of the ocean is the hope you need to hold onto when things are hard.