TITLE: Ms Black, Ms Blue and Ms Green - Is there really a unique answer?
QUESTION [10 upvotes]: This puzzle appeared in an article by Martin Gardner.  It goes like this:
Miss green, Miss Black and Miss Blue are out for a stroll together.  One is wearing a green dress, one a black dress and the other a blue dress.  "Isn't it odd" says Miss Blue, "that our dresses match our last names, but not one of us is wearing a dress that matches her own name".
The question is $$What\ color\ is\ each\ lady's\ dress$$ $$ $$
The solution offered in various places on the net is: $$ $$
$$
\begin{array}{c|lcr}
\text{L/C} & \text{Black} & \text{Blue} & \text{Green} \\
\hline
\text{Ms. Black} & \text{.} & \text{Y} & \text{.} \\
\text{Ms. Blue} & \text{.} & \text{.} & \text{Y} \\
\text{Ms. Green} & \text{Y} & \text{.} & \text{.}
\end{array}
$$
$$ $$
This gives the impression that this brain teaser has a unique solution but, I don't believe that is the case.  If one reflects the above solution along the diagonal, that produces a second solution which must be correct if the first one was correct.$$ $$
$$
\begin{array}{c|lcr}
\text{L/C} & \text{Black} & \text{Blue} & \text{Green} \\
\hline
\text{Ms. Black} & \text{.} & \text{.} & \text{Y} \\
\text{Ms. Blue} & \text{Y} & \text{.} & \text{.} \\
\text{Ms. Green} & \text{.} & \text{Y} & \text{.}
\end{array}
$$
$$ $$
It seems obvious (to me) that this problem has 2 solutions, not just one, as this brainteaser implies by simply asking "What color is each lady's dress".  That said, I thought I'd ask this question in case there is something I have missed. 
Specifically, does this problem have a unique solution or not ?
Edit
The original puzzle adds $$"so\ what" said\ the\ lady\ in\ black$$
which causes the puzzle to have a unique solution. 
See the answer by lulu below which explains why that statement makes a difference.  I originally omitted that part of the puzzle because I mistakenly read: "so what" said Miss Black, which makes no difference unlike when the question is asked by the lady in black (not Miss Black).

REPLY [30 votes]: As requested in the comments:
Gardner's version of the puzzle ends with a line which is omitted here:  $$\text {"So what?", said the lady in black.}$$
Note:  a reference can be found here.
Somewhat surprisingly, that changes everything.  It adds the information that Miss Blue is not wearing black (as she wouldn't have replied to herself, nor would she have disparaged her own observation).  That makes the solution unique.
Note how delicate this information is.  Had the line been spoken by Miss Black, we'd have learned nothing.  Had it been spoken by "the lady in blue" we'd have learned nothing (as we already knew that Miss Blue was not wearing blue).