I would go for 3!
More relax, uplifting color yet understated enough, passe-partout, very feminine, very flattering, it reads : "I am approachable, enjoyable to speak with, yet modest and well mannered. I feel confident with myself, not hung up about my body. I am warm, inclusive. Comfort is important to me, so I will make you feel comfortable in a conversation. Come on, talk to me! I am fun. "
Here is what the other dresses say to me (given the occasion to which you are planning to wear them). (BTW they all look gorgeous on you, they are all killers, and will not say the same thing in different contexts.) (This is done tongue in cheeks).
Here is what 1 says to me: " Let's cut it to the chase here. I am very professional. I have teeth, and may possibly bite if you don't watch out. I am not completely open, am on my guard, and not ready to reveal my true colors. You won't know what I think. Everything you say may be used against you. Don't you mess with me."
Here is what 2 says to me: "Oh hi! ... Me? Oh, nothing, just a bit tired... Yeah... those functions, you know... I've seen my share... what was it you were saying? Jeez I'm so forgetful tonight. Must be the long flight. (Yawn). Well anyway, keep speaking with me at your own risk. I will most likely tend to be a bit negative. Where's the bar?"
Here is what 4 says to me: "Hello everyone! Don't you worry anymore: I have arrived! I am a very proper person, you know. So proper I may make you feel slightly abashed as we chat. I will tell you about my plans, how I am preparing - over preparing - for three Christmases in advance. Oh, and also, I want to be forgotten. You can look at me, but no need to try to know me.
(From a diplomat's ex-spouse, very very acquainted with formal, semi-formal, "business casual" functions involving royalty and government officials. I also lived in a Muslim country. There was always alcohol served at every reception I went to, but you are correct, it would be best not to drink if in company of official representatives).
PS: all these dresses suit you wonderfully and you are a breathtakingly beautiful woman. I am just trying to get my point across about what seems to be, to my eye, the most appropriate attire for the specific event you are describing).