a little curious about the status of reference

snake

I found a little weird phenomena about the reference shown in the zotero (the firefox version).
See the screenshot I got from my database, (I could not paste a picture, so I uploaded it to my google drive, and shared it to public)
https://plus.google.com/photos/107753268680471966922/albums/5892768435814931361?banner=pwa

I mean, you can see, some of the papers are in a kind of grey color, while others are in real black color, but both of them work fine, no any problem.

I am just curious, what is that mean?
Is anyone know about it?
Thanks

adamsmith

This is typically the result of a search. All attachments and parent items are shown, but only those for which the search conditions are met are in black.

snake

So it is. I see :)
Thank you very much for your prompt and concisely explanation.