How do you say Yes a blue pen in French?

This question is a bit tricky! You can't literally say "Yes a blue pen" in French.

Here's how you could express it in French, depending on the context:

1. If you're confirming that you have a blue pen:

* Oui, j'ai un stylo bleu. (Yes, I have a blue pen.)

2. If you're asking for a blue pen:

* Pouvez-vous me donner un stylo bleu ? (Can you give me a blue pen?)

* J'aimerais un stylo bleu, s'il vous plaît. (I would like a blue pen, please.)

3. If you're simply stating the existence of a blue pen:

* Il y a un stylo bleu. (There is a blue pen.)

Let me know if you had a specific situation in mind, and I can help you phrase it more accurately!