Even with tools such as Adobe Photoshop, this is not something that you can normally do to the average photo without first "tweaking" the image.
Sure, you can say "replace all the yellow paint with light green". The problem is, in a photo, the variations in "yellow" are *ENORMOUS*. Part of the house that is in bright sunlight will be one shade of yellow and part of the house that in shade will be another shade. In fact, it may not look like yellow, at all. It may look more like gray or perhaps even brown or green. And what about faded spots or shadows?
Sure, a human with some experience with Photoshop can do this in a few minutes of work, but to expect an untrained person to be able to do it? Or expect a program to be able to do it?
Here's an example: The original photo:
And a naive attempt to replace the basic green color of the church with yellow. Note that this is actually the result of 6 separate replacements. After one replacment, only a very small part of the green was converted.
Doesn't look very good, does it? And this was actually a fairly mono-colored building.
So... Maybe you can get it to work. I'm very skeptical.