Quick answer: Unreal scene capture's render target clear color visible in the final frame as a tint? Clear color is in linear space - convert to sRGB or use a fully opaque clear.

Set RenderTarget ClearColor to mid-gray (0.5, 0.5, 0.5, 1). Composited result has a noticeable grey wash.

Set sRGB-correct clear

RT->ClearColor = FLinearColor(0.214f, 0.214f, 0.214f);

Mid-gray sRGB is ~0.214 linear. Use the linear value for ClearColor; UE doesn't auto-convert.

Or clear alpha to zero

If the RT is composited additively, clear color doesn't matter but alpha must be zero. ClearColor = FLinearColor::Transparent.

Verify with the buffer visualizer

r.SceneCapture.CompositeMode 2 + buffer visualizer shows the RT pre-composite. Tint should match your intent.

“Color spaces in Unreal are explicit. Clearing 'gray' requires knowing which gray.”

Centralize RT setup in a helper that takes an sRGB color and converts. Lots of bugs collapse to this one path.