Chicago
While RS2K is without a doubt both very helpful and "the" verification service in Chicagoland, it is entirely erroneous to state that without such a membership "most 'black tie' ladies won't even reply" to a gentleman. The OP is specifically seeking someone who is capable of blending in and holding her own in a black tie affair.
In other words, he is looking for someone who is apt as a true social companion, and not merely (and here I am going to indulge in a little semantics play, because I believe there to exist a genuine divide) a provider. There exist only a small number of these former individuals, and even smaller still are those who have either the experience or breeding to not raise eyebrows at a genuinely formal affair; I'd imagine the last thing this gentleman wants is for people to know without a doubt that the lady on his arm is a paid companion (wonder about, perhaps, but that's a horse of an entirely different color 
).
Nine times out of ten, those sorts of ladies simply don't run with verification service only screening options. If they did, they would cut their business in half, simply because many (not all, but certainly many) individuals who seek ladies for long extended visits outside of the bedroom simply aren't comfortable or interested in leaving their information on file with a large verification service.
Please don't misunderstand me-I enjoy and benefit from RS2K, and I trust Cathy implicitly. When a gentleman presents me with his membership information or RS2K or one of the other two verification websites, it cuts my work down immensely. However, this doesn't change the nature of the beast. Many men seeking social as well as personal companionship aren't interested in joining such sites, and as a result, many such ladies allow for a wider array of screening options than this. RS2K is wonderful, but it's not an absolute necessity for this gentleman's particular needs.
I would venture to say that she would be an outstanding choice for your formal event.
As well as any "informal" event efterwards 
Including black tie events. And your race is no issue. I'm brown skinned myself and attractive. I know how to dress the part and look elegant when I need to. Some people say I favor Beyonce. I'm sure we would look fabulous together.
Further, I've interacted with people of almost all social and economic backgrounds throughout my life (I have an interesting upbringing) and work experience, so I have no problem mingling with all sorts of people.
And there's my plug.