“I saw a white praying mantis in my garden, and a few days later, I saw a praying mantis about the same size, but it was green. Was it the same one? Can they change color?”
It could have been! One of our circulation clerks happens to raise mantis nymphs as a hobby, and she told us that, depending on the species, mantids can change color as they molt. Like caterpillars and many other bugs, their exoskeletons do not grow with their bodies, and must be shed in order for the mantids to grow. Once they are adults, they will no longer need to do this. An adult mantis can be distinguished from a young one by the wings, which only adults have.
Mantids may turn pale for a while immediately after shedding their skin, which may have been what our patron saw. Molting is a delicate time for them and they should not be disturbed. However, if our patron saw the same mantis later, it seems to have survived the process.