She has no real official dress color (though the line almost exclusively shows her in pink and I actually think Disney meant to keep it blue, hence where she wears that the most but the franchise didnt care) or any, really. I just associate her with the dull colors of the background, kinda. I wish her color was light purple- light for her personality and looks, and purple for her eyes, magical heritage, and because it would just look great on her. I do associate her with the blue dress, however, just because it suits her more- for looks as well as her calm personality.

Maybe I'm looking too into it but you could also say that Merriweather passes on some of her confidence when she wears her blue dress.

Or pink.

I hate that they put her in pink...in my mind, her colour is dark blue.