Go to some coordinates very high above ground (Doesn't always work) and your hands and items in them turn black.
For instance, you can turn your hands dark by /tp-ing into the height of 2100
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duplicates 1
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It happens during the day. Look at the 2nd screenshot.
Resolve forward to MC-194878.
From your screenshot it looks pretty late at night. Are you sure it isn't just caused by that?