What is a mi gusta un rojo mean?

"Mi gusta un rojo" is grammatically incorrect in Spanish. It seems like you're trying to say "I like red," but the sentence structure is off.

Here's how you would say "I like red" in Spanish:

* Me gusta el rojo. (Formal)

* Me gusta el color rojo. (More specific)

* Me gusta el rojo. (Informal, but still correct)

Let me know if you have any other Spanish phrases you want to translate!