Green-tinted pictures...?

This morning, I was preparing to take some indoor shots of a few screws – but they turned out green! Here's exactly what happened:

First, camera/equipment were set up. Then, I arranged the subjects and prepared a Custom WB.

After taking the first image, it came out as shown in attachment #1. I switched WB's and the results are attachments #2 and #3.

#4 is Custom again.

After re-setting Custom, everything went back to normal color. (#5).
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Anyone else had this unnerving experience or thoughts/suggestions about why it occured?