Put it into to Photoshop and eye-dropper the colours. They are quantitatively light blue and dark brown.
But they can perceived as either blue and black or white and gold.
You're assuming proper white balance at the time the photo was shot for the lighting conditions of the environment in which the photo was shot for your "quantitatively" assertion. Unless you were there or took the photo, you cannot say with any certainty.
No, gmbrg is making a statement about the colors recorded in the image file, not about the colors of the dress. The values in the image file are precise quantities.