[patch] Fix sRGB/linear color-space slips in ThemeProvider

ThemeProvider/ColorRange.cs

@@ -19,10 +19,15 @@ public readonly record struct ColorRange(Color Start, Color End)
 	/// </summary>
 	public double Distance => Start.DistanceTo(End);
 
+	/// <summary>
+	/// The perceptual (Oklab) distance below which the start and end colors are treated as a single color.
+	/// </summary>
+	private const double SingleColorDistanceThreshold = 1e-6;
+
 	/// <summary>
 	/// Indicates whether this range represents a single color (start equals end).
 	/// </summary>
-	public bool IsSingleColor => Distance < double.Epsilon;
+	public bool IsSingleColor => Distance < SingleColorDistanceThreshold;
 
 	/// <summary>
 	/// Creates a color range from two colors, automatically ordering them

ThemeProvider/SemanticColorMapper.cs

@@ -177,8 +177,7 @@ private static double CalculateTargetLightnessForSemantic(
 
 		if (allPriorities.Length == 1)
 		{
-			double globalCenter = (globalMinLightness + globalMaxLightness) / 2.0;
-			return meaning == SemanticMeaning.Neutral ? globalCenter : globalCenter;
+			return (globalMinLightness + globalMaxLightness) / 2.0;
 		}
 
 		// Calculate position in range (0.0 to 1.0)

ThemeProviderDemo/Program.cs

@@ -754,19 +754,19 @@ private static IReadOnlyDictionary<SemanticColorRequest, Color> GetCompleteMappi
 		return cachedCompletePalette;
 	}
 
-	private static Vector4 ToImVec4(Color color, float alpha = 1.0f)
+	private static Vector4 ToImVec4(Color color, float? alpha = null)
 	{
 		Srgb srgb = color.ToSrgb();
-		return new Vector4((float)srgb.R, (float)srgb.G, (float)srgb.B, alpha);
+		return new Vector4((float)srgb.R, (float)srgb.G, (float)srgb.B, alpha ?? (float)color.A);
 	}
 
 	private static Color AdjustBrightness(Color color, float factor)
 	{
-		Srgb srgb = color.ToSrgb();
-		return Color.FromSrgb(
-			Math.Clamp(srgb.R * factor, 0.0, 1.0),
-			Math.Clamp(srgb.G * factor, 0.0, 1.0),
-			Math.Clamp(srgb.B * factor, 0.0, 1.0),
+		// Multiplicative brightness is a linear-light operation; scale the linear channels, not the gamma-encoded sRGB ones.
+		return Color.FromLinear(
+			Math.Clamp(color.R * factor, 0.0, 1.0),
+			Math.Clamp(color.G * factor, 0.0, 1.0),
+			Math.Clamp(color.B * factor, 0.0, 1.0),
 			color.A
 		);
 	}