1. "Avoir du rouge": This is the most literal translation, meaning "to have red." You would use this if you are talking about having something that is red, like a red shirt or red paint.
Example: J'ai du rouge à lèvres. (I have red lipstick.)
2. "Être rouge": This means "to be red" and implies that something is red in color. You would use this if you are talking about someone's face being red, or a red apple.
Example: Ses joues sont rouges. (His cheeks are red.)
3. "Avoir les cheveux roux": This literally means "to have red hair," but is commonly used to say "to have red hair."
Example: Elle a les cheveux roux. (She has red hair.)
4. "Être rouquin": This means "to be red-haired," and is a more informal way to say "to have red hair."
Example: Il est rouquin. (He is red-haired.)
The best way to say "have red" in French will depend on the specific context of your sentence.