The answer is :
A population of birds with red feathers slowly changes to having blue feathers
Microevolution is a change in allele frequencies and can be caused by mutations, selection (natural and artificial), gene flow or genetic drift.
What's different from macroevolution is that this change happens over a shorter time when compared to macroevolution which is when big differences in the population happen.
From the options, a change in the colors of fethers seems like a microevolution that happened due to a mutation in the population over a period of time.
