Hi.The color is environmentally determined. Lower humidity and a general "brownish" appearance of their enclosure causes most Parasphendale to get brown in captivity. When kept in living plants in a greenhouse etc. some of them well become greenish.
Regarding the size, most mantids can indeed get larger in captivity due to a better food supply. I compared many WCs with their self-bred progeny and sometimes noticed that mines were larger. Usually you get a variety of sizes around a statistical mean. Why your T. aridifolia are smaller than the WCs is an interesting point. I saw similar size differences in M. religiosa and they can partially be explained by suboptimal parameters: both species are strictly saisonal due to the winter, and if they hatch too late or grow too slow they can "decide" to skip a molt to become adult in time. Those specimens are smaller than ones with a regular number of molts. They may be also other reasons for the size differences, though.
Regards,
Christian