Yeah, don't worry, you're supposed to be able to see they're different.
The majority of the image being grey is gives your brain the right context required to perceive each half is being tinted, so the perceived white balance isn't shifted around like in the original "the dress" meme.
This is more of a teardown of the "original" illusion than a demonstration.
Looking at the bridge, it becomes clear that even though you can see in the wider context that the dresses are separate colours - when compared directly under skewed/tinted white balance they become indistinguishable.
Meaning that in the original "the dress" meme, how you perceived the dress' colour depended greatly on how you perceived the tint/white balance in the surrounding areas of the photo (or how it was displayed on your device).