Okay, this is getting dumb. Lily's often acting like she's not blind at all. This is far from the first example, and I'm not talking about the colour. It feels like the mangaka keeps forgetting about their own gimmick.
@Trevoga Yeah i thought that too and then lily hugged heath and then i forgot about it, probably just a hindsight on the author's part but somethings were explained in lily's past story on how she tried her best and it resulted in her seeming like she wasn't blind... but the color thing was stupid, WELL SHES CUTE SO I FORGIVE
@PantsuKami The color/shape of the dresses were probably just described to Lily beforehand so she could choose it, thus she knew exactly what color the dress was that she herself chose. As another comment mentioned she wasn't blind from birth so its not a huge leap to think she has a grasp on some colors.