Compositing weird colors

Hello, I’m pretty new at compositing but i got some ideas in how to use this, but i cant never manage to solve this particular problem:


As you can see the background is black and it supposed to be blue, and if you watch closely, there’s like a deep blue edge that shouldn’t be there.

I only work in cycles and I’ve been trying to simulate mist using the Z property of the render but i almost never manage to make it correctly due to that problem, I mostly always just grab the Z property and mix it with a math converter to multiply it by 0.01 in order to simulate mist. But this technique never works with colored mist… Is there a way to do this much easier?

Thank you.

show us the node map. also this should be posted under Compositing and Post Processing


As i said before i SUCK, im trying to make it blur in the distance plus the underwater mist.

…Any help?

What’s in the alpha? It could be a premultiplication issue.
Can you send the file?