fix: assign part colors to drawings created by BOM importer and MCP

Drawings created by BomImportForm and MCP InputTools were missing color
assignments, causing them to render with default empty color instead of
the standard part color palette. Moved PartColors and GetNextColor() to
Drawing in Core so all consumers share one definition.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

OpenNest.Core/Drawing.cs

@@ -12,8 +12,32 @@ namespace OpenNest
     public class Drawing
     {
         private static int nextId;
+        private static int nextColorIndex;
         private Program program;
 
+        public static readonly Color[] PartColors = new Color[]
+        {
+            Color.FromArgb(205, 92, 92),    // Indian Red
+            Color.FromArgb(148, 103, 189),  // Medium Purple
+            Color.FromArgb(75, 180, 175),   // Teal
+            Color.FromArgb(210, 190, 75),   // Goldenrod
+            Color.FromArgb(190, 85, 175),   // Orchid
+            Color.FromArgb(185, 115, 85),   // Sienna
+            Color.FromArgb(120, 100, 190),  // Slate Blue
+            Color.FromArgb(200, 100, 140),  // Rose
+            Color.FromArgb(80, 175, 155),   // Sea Green
+            Color.FromArgb(195, 160, 85),   // Dark Khaki
+            Color.FromArgb(175, 95, 160),   // Plum
+            Color.FromArgb(215, 130, 130),  // Light Coral
+        };
+
+        public static Color GetNextColor()
+        {
+            var color = PartColors[nextColorIndex % PartColors.Length];
+            nextColorIndex++;
+            return color;
+        }
+
         public Drawing()
             : this(string.Empty, new Program())
         {

OpenNest.Mcp/Tools/InputTools.cs

@@ -112,6 +112,7 @@ namespace OpenNest.Mcp.Tools
 
             var drawingName = name ?? Path.GetFileNameWithoutExtension(path);
             var drawing = new Drawing(drawingName, pgm);
+            drawing.Color = Drawing.GetNextColor();
             _session.Drawings.Add(drawing);
 
             var bbox = pgm.BoundingBox();
@@ -155,6 +156,7 @@ namespace OpenNest.Mcp.Tools
                     if (pgm == null)
                         return "Error: failed to parse G-code";
                     var gcodeDrawing = new Drawing(name, pgm);
+                    gcodeDrawing.Color = Drawing.GetNextColor();
                     _session.Drawings.Add(gcodeDrawing);
                     var gcodeBbox = pgm.BoundingBox();
                     return $"Created drawing '{name}': bbox={gcodeBbox.Width:F2} x {gcodeBbox.Length:F2}";
@@ -164,6 +166,7 @@ namespace OpenNest.Mcp.Tools
             }
 
             var drawing = shapeDef.GetDrawing();
+            drawing.Color = Drawing.GetNextColor();
             _session.Drawings.Add(drawing);
 
             var bbox = drawing.Program.BoundingBox();

OpenNest.Training/Program.cs

@@ -79,21 +79,7 @@ int RunDataCollection(string dir, string dbPath, string saveDir, double s, strin
         Console.WriteLine($"Using template: {template}");
     }
 
-    var PartColors = new[]
+    var PartColors = Drawing.PartColors;
-    {
-        Color.FromArgb(205, 92, 92),
-        Color.FromArgb(148, 103, 189),
-        Color.FromArgb(75, 180, 175),
-        Color.FromArgb(210, 190, 75),
-        Color.FromArgb(190, 85, 175),
-        Color.FromArgb(185, 115, 85),
-        Color.FromArgb(120, 100, 190),
-        Color.FromArgb(200, 100, 140),
-        Color.FromArgb(80, 175, 155),
-        Color.FromArgb(195, 160, 85),
-        Color.FromArgb(175, 95, 160),
-        Color.FromArgb(215, 130, 130),
-    };
 
     var sheetSuite = new[]
     {

OpenNest/ColorScheme.cs

@@ -13,21 +13,7 @@ namespace OpenNest
         private Color edgeSpacingColor;
         private Color previewPartColor;
 
-        public static readonly Color[] PartColors = new Color[]
+        public static Color[] PartColors => Drawing.PartColors;
-        {
-            Color.FromArgb(205, 92, 92),    // Indian Red
-            Color.FromArgb(148, 103, 189),  // Medium Purple
-            Color.FromArgb(75, 180, 175),   // Teal
-            Color.FromArgb(210, 190, 75),   // Goldenrod
-            Color.FromArgb(190, 85, 175),   // Orchid
-            Color.FromArgb(185, 115, 85),   // Sienna
-            Color.FromArgb(120, 100, 190),  // Slate Blue
-            Color.FromArgb(200, 100, 140),  // Rose
-            Color.FromArgb(80, 175, 155),   // Sea Green
-            Color.FromArgb(195, 160, 85),   // Dark Khaki
-            Color.FromArgb(175, 95, 160),   // Plum
-            Color.FromArgb(215, 130, 130),  // Light Coral
-        };
 
         public static readonly ColorScheme Default = new ColorScheme
         {

OpenNest/Forms/BomImportForm.cs

@@ -420,6 +420,7 @@ namespace OpenNest.Forms
 
                         var drawingName = Path.GetFileNameWithoutExtension(part.DxfPath);
                         var drawing = new Drawing(drawingName);
+                        drawing.Color = Drawing.GetNextColor();
                         drawing.Source.Path = part.DxfPath;
                         drawing.Quantity.Required = part.Qty ?? 1;
                         drawing.Material = new Material(material);

OpenNest/Forms/CadConverterForm.cs

@@ -19,7 +19,7 @@ namespace OpenNest.Forms
 {
     public partial class CadConverterForm : Form
     {
-        private static int colorIndex;
+
         private SimplifierViewerForm simplifierViewer;
         private bool staleProgram = true;
 
@@ -622,7 +622,7 @@ namespace OpenNest.Forms
                     continue;
 
                 var drawing = new Drawing(item.Name);
-                drawing.Color = GetNextColor();
+                drawing.Color = Drawing.GetNextColor();
                 drawing.Customer = item.Customer;
                 drawing.Source.Path = item.Path;
                 drawing.Quantity.Required = item.Quantity;
@@ -671,12 +671,7 @@ namespace OpenNest.Forms
         }
 
 
-        private static Color GetNextColor()
+        private static Color GetNextColor() => Drawing.GetNextColor();
-        {
-            var color = ColorScheme.PartColors[colorIndex % ColorScheme.PartColors.Length];
-            colorIndex++;
-            return color;
-        }
 
         private static bool IsDirectoryWritable(string path)
         {