Hi. I have a clip of some art works on a wall. The clip is moving from right to left showing the art work. I want to change the colors of one of the art works. I have some key points with different color settings, but when i do that it of course applies to the whole picture. How can I make an effect to only apply to certain area, if that area is moving. Should I motion track and mask? I'm very new to After Effects so if anyone could dummy this out, it would be great.
Duplicate the layer, mask out the area you want to change and apply the effect to that layer only.
The method that Mylenium mentions will work, but it's not the only way. You can also use an effect mask, which constrains the area affected by an effect to just be within a mask. Or you could put the mask on an adjustment layer.
I recommend that you start here to learn the basics: