Except for that 25% of the time when they are:
First, Wells argues that the story is seriously flawed because "peppered moths in the wild don't even rest on tree trunks" (:138). He repeats this point throughout the chapter. However, it is both false and irrelevant, and only serves as a distraction to lead the reader away from the actual story of the moths. Contrary to Wells's assertions, data given by Majerus (:123) indicate that the moths do indeed rest on the trunks of trees 25% of the time. The rest of the time moths rest in branches (25%) or at branch-trunk junctions (50%). The facts have been pointed out repeatedly to Wells; his response has been mostly to claim that moths don't rest on "exposed" tree trunks (). But this is not what he said in the text of Icons, which remains flatly wrong. Moths are found all over trees, which is not a surprise () and it is mentioned in the references that Wells cites.
To clear up any confusion, no researcher doubts that the peppered moth rests in trees (; ), which means that the resting substrate is bark. Entire trees are stained by pollution -- the leaves, twigs, branches, trunks, and the surrounding ground () -- and so the colors of the moths are relevant no matter where on the tree they rest -- trunks, trunk-branch junctions, branches, twigs, and even the leaves. Wells's argument implies that predatory birds can only see moths that are on exposed trunks. By making this argument, however, Wells shows an apparent ignorance of the ecology of birds and woodland ecosystems. If you walk into any forest, you can see that the birds fly from tree to tree, branch to branch, and hunt at all levels of the forest. Woodland species of birds that prey on moths and other insects live and hunt in the canopy (the leafy part of the trees). These birds are not hunting from outside, soaring above the trees like hawks, as Wells's argument would require.
In the scientific literature, there is extensive discussion of the hunting behavior of birds, including those that hunt peppered moths. Ornithologists have shown the woodland ecosystem to be vertically stratified by competition between different bird species. This zonation means that there are skilled predators patrolling all levels of the forest: the trunks, trunk-branch joints, branches, and higher canopy (; ). Further, birds learn to distinguish their prey against various backgrounds and preferentially hunt prey in locations where they have found it in the past and that birds selectively prey on the more visible moths (, ). In other words, birds hunt the prey they can see and hunt it where it is, not where it isn't. Therefore, no matter where the moth rests in the tree, it is visible to predatory birds, and thus its differential camouflage is important.
It is not false, otherwise the phony 'scientist' that pasted them up would not have had a need to commit a fraud, he could just have photographed them any time. It is not irrelevant, because the moths are very hard to see if they perch in the branches of the trees and the coloring would not matter very much in such cases. So you are wrong on both counts.
Regardless, this is not an example of evolution, indeed it is not even an example of speciation. Both kinds of moths existed before the industrial revolution and both kinds exist after the cleanup of the smoke stacks.