user4491: I have this shot which has the right door color corrected to make it look dark and red :

How would I go about making it part of the "background" so that when someone comes in front of it, he is not affected by the correction like in the shot below :

I tried looking into Masks as background or 3D layers but couldn't seem to find what I'm looking for. I'm sure it's an easy thing to do but I just need guidance on what to look / search for.

user11523: You need to rotoscope every object in front of your "background". There is not simple solution, because AE cant tell the difference between you foreground and background. Even I can't tell, because people drop shadows on your "background", etc.
You can try to use rotobrush for that, but if you have there a lot of people, it will require a lot of work.

4491: <p>I have this shot which has the right door color corrected to make it look dark and red :</p>

<p><a href="https://i.stack.imgur.com/4IEmQ.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/4IEmQ.jpg" alt="enter image description here"></a></p>

<p>How would I go about making it part of the "background" so that when someone comes in front of it, he is not affected by the correction like in the shot below :</p>

<p><a href="https://i.stack.imgur.com/yyGHY.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/yyGHY.jpg" alt="enter image description here"></a></p>

<p>I tried looking into Masks as background or 3D layers but couldn't seem to find what I'm looking for. I'm sure it's an easy thing to do but I just need guidance on what to look / search for.</p>
 11523: <p>You need to rotoscope every object in front of your "background". There is not simple solution, because AE cant tell the difference between you foreground and background. Even I can't tell, because people drop shadows on your "background", etc.</p>

<p>You can try to use <a href="https://helpx.adobe.com/after-effects/using/roto-brush-refine-matte.html" rel="nofollow noreferrer">rotobrush</a> for that, but if you have there a lot of people, it will require a lot of work.</p>
