All the fans in both GH's run from 9:00AM until 4:00PM. No variable there. I don't know. They have been growing side-by-side in the same GH since mid-October. The yellow one has been on the porch for three weeks, but hanging in a clear-vinyl covered, 6'x30' east-facing porch (window). The coppery one came in about a week ago. I would have thought that whatever influences color would have occurred long before they came in.
You are right, I will know whether this persists when they bloom again in the late spring/early summer. I just need to put a "yellow" tag on that one so I know the difference. Of course, I may not even have them both by then. That would not be a surprise. In that case, I will never know.
