The hair color and maybe the height are most likely mistakes. Also from the artist's description at Tor.com it seems that the woman on the left is supposed to be Elayne, since she states: "When you add in the thumbnail-size that ebook covers are often first seen at, I thought it best to focus on a few of the key characters: Elayne, Aviendha, and Nynaeve."
She obviously names the women in the picture from left to right.

The artist also explicitly mentions that she was especially informed on the correct clothing for the women, thus it's unlikely that she would give Elayne and Aviendha a wrong dress.