The sky is blue.

Source: Tatoeba

This flower is yellow, but all the others are blue.

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If you mix blue and red, you'll get purple.

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Sulfur burns with a blue flame.

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This blue sweater is very pretty.

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He thinks that blue is the most beautiful colour.

Source: Tatoeba

Is this blue?

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Do you know why the sky is blue?

Source: Tatoeba