Black outline around pre-comp when using a solid or shape as a background.

[alecfrancis]

These pre-comps are identical but the one on the left has a solid being used as a background turned off and the other one has it on. why is this black outline showing on the one on the right, it shows up in renders.

[Mylenium]

Start by viewing your artwork at 100%. This could be a fluke. That said, it probably has more to do with your track matte at the bottom than the background itself. I'm pretty certain it's some semi-transparent pixels from the matte only showing up under certain conditions and that can probably be fixed easily by treating it with Simple Choker or such.

Mylenium

[alecfrancis]

The black outlines only appear at certain percentages. and it's random, and sometimes part of or all of the line will disappear, but it still appears in the render itself. 

I don't think it's the track matte. here is the same comp with only  a random shape layer inside of it, and the outline in the comparison comp 

[alecfrancis]

Also applying a simple choker makes the line disappears in after effects but rendering the video still results with the black line appear 

[alecfrancis]