I have been putting my poinsettias in darkness for 12 to 14 hours a night for several weeks. I have a 6-year-old red one and a 3-year-old variegated pink one similar to the picture above. I was not successful in getting them to bloom last year because I wasn't devoted enough to give them the darkness they needed. I'm hoping I have solved that problem this year.
It may be too soon to tell, but I think I can see tinges of red on the large one tonight. If I manage to force them into blooming they will be a spectacular sight. The oldest stands close to 4-feet tall and the youngest is about 2 1/2 feet tall.
I'm thinking I need to add another color to my collection this year, but I haven't decided what color I want.
Until Next Time .... HAPPY GARDENING!
UPDATE (11/23): It's only been 3 days since my post and I'm happy to say that I now have several small red leaves on the red poinsettia. The variegated pink poinsettia has a few leaves that are beginning to look a little splotchy. I assume they are beginning to change color and should be showing some pink soon!