1. Formal/Respectful:
* આપનો પ્રિય રંગ કયો છે? (Aapno priya rang kayo chhe?)
2. Informal/Casual:
* તારો ફેવરિટ કલર કયો છે? (Taro favorite color kayo chhe?)
Both translations are correct, but the choice depends on the context and the relationship between the speaker and the listener.