Check your Shaders to make sure you don't have any 0-255 or 16-235 added and check your Output Range setting (Right-click, Render Settings/Output Range - 0-255).
Also check your driver control panel to make sure you aren't forcing a color range on video players, AMD no longer has these controls as of Crimson
To quadruple check I switched to the ffmpeg encoder and the results were the same.