Question on how Evolution works to produce new characteristics

Just to break your question down in a few pointsInitially1) Frogs are all green
2) Flora is all greenAftera) Frogs are all green
b) Flora is mixed colourOk the first problem with your question is that that not said what the selective pressure is (though I'm assuming that its predation) because without some form of selective pressure that operates on colour there is no reason why any particular colour will be favoured by seleciton. Genes are only conserved when there is a selective pressure weeding out mutations (Neutral mutation aside which have no effect on a genes function) so its likely that (Assuming a mutation in the genes that control the frogs colour aren't also involved in something that would prove fatal if a mutated) that there may be some variation in colour already unless there was predation.For you're question we'll need to make a few assumptions

1. There is predation and that predator hunts by colour vision
2. The genes responsible for frog skin colour:
   1. produce different colours following mutation
   2. are not linked to something else in the frog that if changed via mutation would be fatal.
3. There is sufficient time for the neccesary mutation to take place. Extinction is the alternative if a species is unable to evolve quickly enough to keep up with environmental change.

For what you propose to happen a frog would need to have a mutation in the genes that controls its skin colour which results in it being slighty better camouflaged than others of its kind. The result being that this individual has a greated chance of surviving predation and therefore reproducing and passing its genes on. Depending on how great an advantage this mutation gives an individual will affect how quickly it spread through the population but I understand that beneficial mutations can become common in a population very quickly. There may be further mutations within the population which in turn make individuals slightly more better camouflaged and the same process happens again.Assuming that the assumptions I made above are met then yes the island would be dominated by the speckled (Or more likely whatever the mutation resulted in) skin. Evolution has no forsight and therefore doesn't decide what will be the best camouflage. It simply selects the best at surviving in a given population and by doing so ensures the genes that gave them that advantage get passed on.In my opinion extinction would be the most likely outcome if its an issue of predation. Just look at the effect which alien predators have had on Australian fauna in a short period of time.Edited by Asking, : Forgot to mention nuetral mutationsEdited by Admin, : Fix list to use dBCodes.