When breaking a block that is under another block, some of the particles will be very dark. This only happens when breaking a block that is under another, as far as I can tell.
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[media]
Similar to/Duplicate of MC-48724
It is similar to the torch particle bug that I also reported, but since you can only report one issue per bug, I decided to make it a separate report and I couldn't find it by searching so I don't think it's been reported yet. It's kind of hard to notice right off the bat. I didn't notice it until hours of playing 14w08a.