What do 1,000 small changes within a species add up to?
What happens when the small changes result in nonviability of offspring between two distinct members of a species?
That causes a new species. That's evolution.
If a change in color can happen over the course of a few generations, what about 10,000 generations, especially if those changes aren't species-wide, but localized?
Could it happen to be that the sex organs of these specimens fail to couple together properly? Could that ever happen with microevolution?
That's not even a real question. The answer is YES.
Over time there will be no interbreeding at all between the two groups, and their microevolutionary changes will add up to marco differences, and eventually they will be incapable of producing offspring even with artificial fertilization.
Microevolution IS macroevolution.