I understand that. A creature will find a niche and by adapting to it. Those adaptations are from mutations that are beneficial to it adapting and surviving. It happens through gradual changes that are taken on.
But like when evolution uses the example of say a creature growing hair in a cold climate to keep warm when it didn't have any hair before. With this example you can see how that would work. Hair follicles are stimulated into growth and they grow hair. The same as the English moth that evolutionist like to use as evidence of transition. The moth changed from a light moth to a dark moth when the trees went darker from the pollution. Though i dont see that as a transition but merely a feature it already had within its DNA.
Now with the butterfly that has the picture of what looks like 2 flies on its wings well that is different. You are saying that chance and random mutations created the picture of 2 flies eating a flower or whatever they are eating. So along the way to get that picture the shapes that would have been used were produced by random stages which would not have been anything to do with the picture of a fly but just a random blotch or mark. That first mark was still beneficial because it gave it some advantage but it had nothing to do with a picture of a fly.
So the mutations is still taken on for another reason. But we know that the reason has something to do with putting the picture of an insect on its wings to scare off predators or something to do with mating. More likely its a defense of some sort as the flies or insects stand out as looking like its a different insect sitting there, perhaps one that is more mean looking or to make it look like something else to the particular predator that is after it.
Creatures in nature have certain features that mimic other creatures. They may have camouflage like the stick insect that looks like a twig. They may make themselves look like something uninviting or dangerous. As it turns out the fly pictures are more than likely a particular fly like the sarcophagid flies. Eating these can result in myasis (maggots in your innards), since the females produce maggots (rather than eggs), which escape from the mother when she is injured, and could do so in the oesophagus, where they could cause some real damage. Not such edible fare! This is just a hypothesis and has to be tested but it is very interesting.
The actual picture on the moth is suppose to represent two flies eating some bird droppings. They say it even puts off a smell like bird droppings as well. Even the white bits on the wings are suppose to represent the light reflecting from its wings to make it look real. So it just seems like these creatures are getting these features from more than mutations. They seem to have some intelligence about it. They know which creatures to imitate in some detail and suggests they know what is best to take on for their particular situation. There are just to many things that have gone right or fallen into place and a knowledge of what sort of creatures it should mimic to be random and chance. The fly is not just any old fly made up of gradual blotches that go together like a jig saw puzzle. Its a particular fly for a particular reason. That to me speaks of an inbuilt ability to have this defense and knowledge to produce that particular picture in one go to ward off predators.
http://www.myrmecos.net/2011/08/30/a-mural-on-moth-wings/