Quick answer: Godot 4 C# [Export] Color property saved with alpha = 1 regardless of inspector input? PropertyHint default doesn't include alpha - use [Export(PropertyHint.ColorNoAlpha)] inversely or explicit alpha.
Set inspector color to (1, 1, 1, 0.5). Reopen; alpha is 1.0.
Use proper PropertyHint
[Export(PropertyHint.None, hintString: "alpha")]Explicit alpha support. Inspector saves the alpha component.
Or use Vector4 instead
Direct Vector4 export. Caller treats RGBA explicitly; no PropertyHint magic.
Verify in .tscn
Open the scene in text editor. Color property should serialize all four components.
“Property hints are typed serialization. Some hints drop data.”
Audit Color exports for the alpha bug. Many projects have it; nobody notices because most use RGB.