V.W.
No, but I could see it happening easily enough. Folks zero in on the information printed within the text of the invite, and don't notice what isn't there. In other words, even if the entire card is pink, they don't notice that there is no blue with it. It just looks "baby" to them, and they don't make any mental notes about the lack of blue.
Also, in this day and age, no one wants to assume anything that isn't specified, so even if someone did notice it was all pink, they wouldn't necessarily make the leap that THAT MEANS that the baby is a girl.
But yeah... the invitees aren't looking for "clues" when they open the invite, and probably wouldn't notice the LACK of other colors unless they ALREADY know the baby is a girl. Then it might be more noticeable.
:)