* Langit na asul (literally "sky that is blue"): This is the most literal translation and emphasizes the blue color of the sky.
* Asul na langit (literally "blue sky"): This is a more common way to say it and emphasizes the sky itself being blue.
* Malinaw na langit (literally "clear sky"): This is a more poetic way to say it, implying a beautiful and unobstructed sky.
All of these phrases are correct and understandable. You can choose whichever one you prefer based on the context of your sentence.