I'm also in team gold and white. Just like you, my brain perceived the source of light is from the back and part of the dress that I saw is shaded.
What helped me see the dress as black and blue is trying to imagine a zoomed out image of this photo where the dress in uncropped, then force myself to believe that it is a brightly lit clothing shop. Also I tried to see the background as a mirror that reflect the light, so my brain can finally process that the lighting is not exclusively from behind the dress.
This is a clear case of rage bait and I realize I knowingly contribute to the proliferation of this tactic by leaving a comment thus increasing traffic metric to this post. Good thing we are all too lazy to click the link and read the post.
edit: everyone who wants to enjoy good contemplative slow-paced episodic anime should watch Mushishi.