About the Preview with Light setting

In the Unreal Engine preview, when I set the light option, the background color appears lighter in the foreground even though the texture color in the additive material is set to (255,255,255) and the transparency is set to 100%. (Without the light, 100% white is rendered as expected.)
Does this mean that the lighted option in the preview is correcting the material’s material color itself to be darker?
My preferred behavior of the lighted preview is to blacken the screen as a post-process rather than interfere directly with the material color.