I'm not sure I understand the reasoning behind your procedure. What does color keying have to do with color correction? That and of course you haven't told us anything about the effects you are using, your version of AE, your system, a screenshot of the layer stack, the source of your EXRs and their specs. A lot can go wrong when using float images and presumably it's exactly that - you are salpping on an 8bit or 16bit effect that cannot deal correctly with out of range values.
Oke let me explain. This is a 3D generated image. It is rendered.
In order to do color correction on different parts individualy i rendered each part of the image
in a solid color to target them to be able to correct only that part of the image.
And to be able to isolate the part that need color correction I used color key to do that.
Sorry for my bad english.
What i use:
After Effect CC 2017
On this image you can see. with the color key i target only the grey.
and in the layer panel you can see the TH_IDs is the solid color layer.
and on this image you can see that i turn of the TH_IDs layer visibility
and put the levels on the TH_AO wich is the original image.
Well, if you 3D-rendered it, you would simply use an Object ID pass or an RGB matte. Otherwise I maintain that you're screwing up the colors by clipping away the internal ranges of your float data. At least you would have to use the Compander effect to bring them within 0-1 ranges and then your awkward keying might even work, but to me your workflow realyl doesn't make the most sense.
Try to set your project to 32bpc. Anyway, if you are using the "Obsolete" Color Key effect, this effect did not process at 32bpc, only 16bpc and it is possible that this could cause your issue. As Mylenium says, there is no reason to do this with color key effects as you can output any Object ID from any 3D package software.
Thaks for your time. But the reason that i had to do it this way is because the renderer I am using the Object ID option is messed up. its not working properly. so i had to find a other way around.
its complicated lol.
It sounds like you resolved your issue. If not, let us know how you solved it. If so, please let us know so we can assist you further.
I did change my workflow. so that solved my prblem.
I wonder if your EXR uses B44 compression, which is lossy and can produce artifacts. In general I would stay away from B44.