Remove Player Light and Spectator Light

Development Rendering
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3

That can have multiple causes:

  1. Your Material has the Lighting Model set to Subsurface or similar, causing the backlight to shine through
  2. the Light/Sun could be reflected. turn the roughness up and the specular down to disable reflections.
  3. Do you have a SkyLight placed in the Map? If so, make sure the lower hemisphere is set to black.