How do I turn a specific color into an alpha channel?

I'v been working on a pseudo 3D dungeon crawling prototype but ran into a snag;

While setting up a dynamic shadow system I came across a problem which, on paper, should be pretty easy to fix yet I can't find the solution I'm looking for.

As you can see the back layer of the front wall bleeds into the sidewall. Normally, it'd just be a question of shifting the sidewall to the front, but doing so would let the shadow go on-top of the front wall.

So the solution I thought of is simply making the back wall's black parts turn invisible depending on the camera's angle, but as far as I'm aware there isn't any effects that can do this.

One other method would be using 2 different animations (One with black, the other without) and switch between them as needed, but I find it way too inefficient considering the size of the textures.

TLDR;

Is it possible to turn a sprite's specific color into an alpha channel?

I appreciate any help I can get!

I don't think masks could be easily be implanted for what I'm doing.

Here's what the walls normally look like in motion;

gph.is/g/4DkoJm9

The front-facing walls have two "Layers" to give the impression of 3D depth.

My current problem is that with my newly implanted shadows, the back layer of those walls are being rendered ontop of the side walls.

My preferable solution to this would be making the back layer's black turn invisible.

So depending on the camera's angle I can toggle this invisibility on/off.

But I'm not sure that's even possible.

The alpha clamp worked!

Thank you very much for this, you've saved me from an headache and a half!