Answer: I assume that you care for them more or less equally, so the difference is probably environmental. Generally speaking they detest warm and cold drafts, prefer humidity and like bright sunny conditions with lower temperatures at night than during the day. Another possibility is pests: check carefully under a bright light for any signs of activity. Look at the undersides of the leaves, along the stem and pay particular attention to the spot where leqves and stems join. Another possibility is that the potting soil is different, causing a problem with watering or nutrients. Finally, in my experience some of the plants, particularly the double flowered bicolors, are simply less robust than the "plain old" pink or red flowered plants and tend to suffer more from moving shock and stress. If this is the case, provide it the best conditions you have and be patient -- it may come around.
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