我想在CAD里按颜色选择实体，请用C#给我一段示例代码

以下是一个简单的示例代码，可以在CAD中按照颜色选择实体：

using Autodesk.AutoCAD.ApplicationServices;
using Autodesk.AutoCAD.DatabaseServices;
using Autodesk.AutoCAD.EditorInput;
using Autodesk.AutoCAD.Runtime;
using Autodesk.AutoCAD.Colors;

namespace SelectEntitiesByColor
{
    public class Commands
    {
        [CommandMethod("SELBYCOLOR")]
        public void SelectEntitiesByColor()
        {
            // 获取当前文档和数据库
            Document doc = Application.DocumentManager.MdiActiveDocument;
            Database db = doc.Database;

            // 获取当前编辑器
            Editor ed = doc.Editor;

            // 提示用户选择颜色
            PromptResult res = ed.GetKeywords("Select color",
                "Red Yellow Green Cyan Blue Magenta White",
                "Red");

            if (res.Status != PromptStatus.OK)
                return;

            // 解析用户选择的颜色
            Color color = Color.FromColorIndex(ColorMethod.ByAci,
                GetColorIndex(res.StringResult));

            // 开始事务处理
            using (Transaction tr = db.TransactionManager.StartTransaction())
            {
                // 打开模型空间
                BlockTable bt = tr.GetObject(db.BlockTableId,
                    OpenMode.ForRead) as BlockTable;

                BlockTableRecord btr = tr.GetObject(bt[BlockTableRecord.ModelSpace],
                    OpenMode.ForRead) as BlockTableRecord;

                // 创建实体过滤器，通过颜色过滤实体
                TypedValue[] filterList = new TypedValue[]
                {
                    new TypedValue((int)DxfCode.Color, color.ColorIndex)
                };

                SelectionFilter filter = new SelectionFilter(filterList);

                // 提示用户选择实体
                PromptSelectionResult selRes = ed.GetSelection(filter);

                if (selRes.Status != PromptStatus.OK)
                    return;

                SelectionSet selSet = selRes.Value;

                // 循环遍历所选实体
                foreach (ObjectId id in selSet.GetObjectIds())
                {
                    Entity ent = tr.GetObject(id, OpenMode.ForRead) as Entity;

                    if (ent != null)
                    {
                        // 处理实体
                        ed.WriteMessage("\nSelected entity: " + ent.GetType().Name);
                    }
                }

                // 提交事务处理
                tr.Commit();
            }
        }

        // 获取颜色索引
        private short GetColorIndex(string name)
        {
            switch (name.ToUpper())
            {
                case "RED":
                    return 1;
                case "YELLOW":
                    return 2;
                case "GREEN":
                    return 3;
                case "CYAN":
                    return 4;
                case "BLUE":
                    return 5;
                case "MAGENTA":
                    return 6;
                case "WHITE":
                    return 7;
                default:
                    return 1;
            }
        }
    }
}

这段代码将提示用户选择颜色，并根据用户选择的颜色过滤实体。然后遍历选择集，处理所选实体。请注意，这是一个简单的示例，并且可能需要根据您的实际需求进行修改。