Adopt validated colorblind-safe palette for Query Store visualizations

src/PlanViewer.App/Controls/QueryStoreHistoryControl.axaml.cs

@@ -59,16 +59,19 @@ public partial class QueryStoreHistoryControl : UserControl
 	private static readonly SolidColorBrush ActiveButtonFg = new(Avalonia.Media.Color.FromRgb(0x11, 0x12, 0x17));
 	private static readonly SolidColorBrush InactiveButtonFg = new(Avalonia.Media.Color.FromRgb(0x9D, 0xA5, 0xB4));
 
+	// Validated colorblind-safe categorical ramp (dark surface), in fixed CVD
+	// order — shared with the Multi QS Overview database palette so the two
+	// Query Store views read as one system.
 	private static readonly ScottPlot.Color[] PlanColors =
 	{
-		ScottPlot.Color.FromHex("#4FC3F7"),
-		ScottPlot.Color.FromHex("#FF7043"),
-		ScottPlot.Color.FromHex("#66BB6A"),
-		ScottPlot.Color.FromHex("#AB47BC"),
-		ScottPlot.Color.FromHex("#FFA726"),
-		ScottPlot.Color.FromHex("#26C6DA"),
-		ScottPlot.Color.FromHex("#F06292"),
-		ScottPlot.Color.FromHex("#A1887F"),
+		ScottPlot.Color.FromHex("#3987E5"),
+		ScottPlot.Color.FromHex("#199E70"),
+		ScottPlot.Color.FromHex("#C98500"),
+		ScottPlot.Color.FromHex("#008300"),
+		ScottPlot.Color.FromHex("#9085E9"),
+		ScottPlot.Color.FromHex("#E66767"),
+		ScottPlot.Color.FromHex("#D55181"),
+		ScottPlot.Color.FromHex("#D95926"),
 	};
 
 	// Map grid orderBy tags to history metric tags

src/PlanViewer.App/Controls/QueryStoreOverviewControl.Donut.cs

@@ -81,12 +81,15 @@ private void DrawDonut()
                 var labelR = (radius + innerRadius) / 2;
                 var lx = cx + labelR * Math.Cos(midAngle);
                 var ly = cy + labelR * Math.Sin(midAngle);
+                // Pick label ink by arc luminance (same rule as the bar cards) so the
+                // percentage stays readable on light fills instead of white-on-light.
+                var labelLuminance = 0.299 * color.R + 0.587 * color.G + 0.114 * color.B;
                 var pctLabel = new TextBlock
                 {
                     Text = $"{pct:F0}%",
                     FontSize = 10,
                     FontWeight = FontWeight.SemiBold,
-                    Foreground = Brushes.White,
+                    Foreground = new SolidColorBrush(labelLuminance > 128 ? Colors.Black : Colors.White),
                 };
                 pctLabel.Measure(Size.Infinity);
                 Canvas.SetLeft(pctLabel, lx - pctLabel.DesiredSize.Width / 2);

src/PlanViewer.App/Controls/QueryStoreOverviewControl.WaitStatsChart.cs

@@ -89,6 +89,7 @@ private void DrawWaitStatsChart()
 
         var stepX = w / n;
         var barGap = Math.Min(2.0, Math.Max(0.5, stepX * 0.1));
+        const double segGap = 1.0; // surface gap between stacked segments so bands stay distinct
 
         for (int i = 0; i < n; i++)
         {
@@ -121,7 +122,7 @@ private void DrawWaitStatsChart()
                 var rect = new Rectangle
                 {
                     Width = Math.Max(1, stepX - barGap),
-                    Height = Math.Max(0.5, segH),
+                    Height = Math.Max(0.5, segH - segGap),
                     Fill = new SolidColorBrush(color),
                 };
                 Canvas.SetLeft(rect, x);
@@ -139,7 +140,7 @@ private void DrawWaitStatsChart()
                 var rect = new Rectangle
                 {
                     Width = Math.Max(1, stepX - barGap),
-                    Height = Math.Max(0.5, segH),
+                    Height = Math.Max(0.5, segH - segGap),
                     Fill = new SolidColorBrush(OthersColor),
                 };
                 Canvas.SetLeft(rect, x);

src/PlanViewer.App/Services/AppSettingsService.cs

@@ -2,6 +2,7 @@
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.IO;
+using System.Linq;
 using System.Text.Json;
 using System.Text.Json.Serialization;
 
@@ -77,6 +78,12 @@ public static AppSettings Load()
             settings.MultiQsTopDbCount = Math.Clamp(settings.MultiQsTopDbCount, 2, 20);
             settings.QueryHistoryMaxPlans = Math.Clamp(settings.QueryHistoryMaxPlans, 1, 100);
 
+            // Migrate installs still on the old default palette to the validated
+            // colorblind-safe ramp. Only touches settings that exactly match the
+            // legacy defaults, so any user-customized colors are left untouched.
+            if (settings.MultiQsTopDbColors.SequenceEqual(LegacyTopDbColors, StringComparer.OrdinalIgnoreCase))
+                settings.MultiQsTopDbColors = new List<string>(DefaultTopDbColors);
+
             _cached = settings;
             return settings;
         }
@@ -174,9 +181,23 @@ public static void RemoveRecentPlan(AppSettings settings, string filePath)
     }
 
     /// <summary>
-    /// Default color palette for Multi QS Overview top databases.
+    /// Default color palette for Multi QS Overview top databases. Eight hues from
+    /// the validated colorblind-safe categorical ramp (dark surface), in fixed CVD
+    /// order. Databases beyond the eighth fold into the neutral "Others" fill, so
+    /// no invented ninth hue is ever needed.
     /// </summary>
     internal static readonly List<string> DefaultTopDbColors = new()
+    {
+        "#3987E5", "#199E70", "#C98500", "#008300",
+        "#9085E9", "#E66767", "#D55181", "#D95926",
+    };
+
+    /// <summary>
+    /// The pre-dataviz default palette. Retained only so <see cref="Load"/> can
+    /// detect an installation still on the old defaults and migrate it to
+    /// <see cref="DefaultTopDbColors"/> without clobbering a user's custom colors.
+    /// </summary>
+    private static readonly List<string> LegacyTopDbColors = new()
     {
         "#2EAEF1", "#F2994A", "#27AE60", "#9B51E0", "#EB5757",
         "#F2C94C", "#56CCF2", "#BB6BD9", "#E91E63", "#00BCD4",