Dr Adequate writes:
As I understood it, the question implies that they are better off by being camouflaged against the vegetation.
...
For my money, given the premises of the question, we would indeed end up with green frogs with orange spots.
And that is where you go wrong. Evolution isn't concerned with what they are better off being, it doesn't work that way. If the frogs get selected for the nasty or toxic ones surviving longer, they might develop the survival method of being garish and poisonous. In that case camouflage might actually be selected against, even though theoretically if they were all camouflaged they would have a higher rate of survival.
The process doesn't run through what is most effective in theory, it needs to work with what it has.