The dress is a bistable picture, similar to the Spinning Dancer, which you can consciously reverse the direction of spin with some practice.
To see the dress as blue-black, I first look at the black dress in the bottom-left corner, then shift gaze to the main dress when colour is established.
To see the dress as white-gold, I first look at the sunny regions on the right, then move gaze across, when the main dress goes to white-gold.
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It may help to cover or mask the opposite region, when focusing on one side.
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For detail, 10 years ago I saw this as white-gold and did not change from that perception. Did not know what all the fuss was about this dress. Today, I saw it as white-gold initially, but 10 minutes later, after two friends saw it as blue-black, I also saw it as blue-black and could not shake it.