Video renders with slight color differentiations (noticeable)

Hi, 

I am having troubles with rendering a video that uses a color matte (#181818 hex code), when the video is rendered it leads to slight variations of (#181818 - #171717 hex code), it occurs across the entire video and happens in a square like form, it can be very noticeable when looked at due to how much of a variation there is. 

Variation 1

Variation 2

Compare when both seen at a video