On this particular plant the light intensity is the same year around - so are watering and fertilizing regimes. It is very definitely the temperature that affects the flower color and I have noticed the same with other hybrids of Sophronitis coccinea. This has been demonstrated with other flowers as well: carnations for example (
http://sciencelinks.jp/j-east/articl...6A0491900.php). Some commercial growers of cut orchids even recommend placing the plants in a cool house for a time before cutting the flowers in order to strengthen flower color.