Answer: If they seem healthy, keep doing whatever you are doing for now! Be careful though that you do not overfertilize them in winter, usually they need no fertilization until mid spring.
The trimming back is done sooner or later in the spring to help control their size and keep them bushy during the summer when they come into active growth again. These are naturally rather large plants, so to keep them from year to year as houseplants means they need to be pruned back. Spring is the best time to prune them. Usually they would be trimmed back by at least half, sometimes even more. You could do it in late spring, or do it earlier if they defoliate and look unkempt as a result of being unhappy with their growing conditions during the late winter months. Apparently they are happy where you have them so you can wait and do it later.
The regrowth during summer will be green. The darkness treatment is used in the fall to make them color up for the holidays; they are sensitive to day length and this is what causes them to turn red.
I hope this clarifies for you.
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