There are several problems arising here. First of all: the tested mantids are not in the wild, but under captive conditions. So you can't expect them to do what they would do in the wild. One point is that the cage as such is a small compartiment, regardless how large it is; and in most such cases space is reduced in favor of sample size. Ever asked why mantids always hang on the mesh? It's not only because they get a better grip, but because it's the highest point (away from the ground) they can reach. Particularly the arboreal species live at a certain height. So, even an understorey species like Deroplatys or Euchomenella perch at about 1-4 m height, that is more space than most people would allow their mantids to live in. The larger the species the more obvious this problem. And the larger the cage, the more the mantids space out in it and aren't confessed to the top screen.The pink/other morphs we are looking for have formed in the wild without such all-or-none conditions. I don't see the benefit in testing a completely colored cage. The 100% color could introduce other environmental stress factors we are not aware of. Even for my casual test with colored post-its and pen markings, it appears that the mantises will tend to stay in areas that are green, green/pink, and pink areas over the clear deli-tub sides or the plain white top areas. Probably better to let them choose where to go...more like they would in the wild.
The point here is: neither does the mantid behave in captivity as in the wild, nor can it choose a perch as in the wild. A typical case are the so-called flower mantids including Hymenopus, who would sit everywhere except on the flowering plants we are offering them.
The other important point is that color change in mantids is induced by an overall impression of the environment. An arborel species always has a green "forest" impression when "it looks around". A grass dwelling species is surrounded by an ocean of light green (or tan, when the grass fades). Our mantids are in a lab or at home and the only impression of the environment they get is tan or grey. Putting a leaf or a pink flower or sheet inside its cage doesn't change the mantid's impression that it lives in a brownish environment. Thus, if you want to see any effect whatsoever, you have to change the mantid's impression of its ovarall captive environment. You have to paint everything in the color you are testing for, or, filter the light in a way as it is, for instance, filtered and reflected by natural foliage.
And here the last obstacle arises: light spectrum. You cannot achieve the full spectrum of natural color changes under artificial lighting. But you get some results and they are worth testing them. In order to achieve natural color changes you have to use a greenhouse with plastic roofing (UV should pass through). You should at least try to get the best spectrum available. The terraristic sector offers some good alternatives in the meanwhile.