Depends on how you define color and you can indeed find various definitions for it. If you only judge by the light reflected and not the brain's interpretation of what the eye caught, that dress is definitely blue and black (admittedly, you would have to have good definitions for blue and black, but I think the most basic wavelength intervals would suffice).
So, from what I understand:
robo -> dress (mostly feminine)
robino (female dress) -> robe (male dress)
I am laughing almost two minutes straight at this...
On a (slightly) more serious note, I would go with banrobo ou duŝrobo, but did not find any reference of both on google.