How do you say A blue dress in French?

There are a few ways to say "a blue dress" in French, depending on the context and formality:

Formal:

* Une robe bleue (This is the most common and formal way)

Informal:

* Une robe bleu (This is more common in spoken French)

* Une robe bleue (This is also acceptable in spoken French)

Other options:

* Une robe de couleur bleue (This emphasizes the color)

The best option depends on the context and who you are talking to. For example, "une robe bleue" would be a good choice for a formal letter, while "une robe bleu" might be better for a conversation with friends.