C1TreeViewには、ノード行の全体のスタイルを設定するためにApplyNodeStylesイベントが用意されています。
バウンドモードでは、イベント引数のe.Node.GetValueを用いてノードのデータソースとなっているDataRowを取得できます。DataRowのフィールド値が指定ノードのデータ値に一致する場合にe.NodeStyles.Default.ForeColor／BackColorプロパティを設定することで、行全体の前景色／背景色を変更できます。

以下に、各ルートノードを異なる色に設定するサンプルコードを記載します。



◎サンプルコード（VB）

Imports C1.Win.TreeView

Public Class Form1
    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load

        C1TreeView1.Columns.Clear()
        C1TreeView1.BindingInfo.DataSource = Nothing

        ' ツリーの設定
        C1TreeView1.BindingInfo.DataMember = "Employees"
        Dim column As C1TreeColumn = New C1TreeColumn()
        column.DisplayFieldName = "Post"
        column.HeaderText = "Post"
        C1TreeView1.Columns.Add(column)
        column = New C1TreeColumn()
        column.DisplayFieldName = "FirstName"
        column.HeaderText = "First name"
        C1TreeView1.Columns.Add(column)
        column = New C1TreeColumn()
        column.DisplayFieldName = "LastName"
        column.HeaderText = "Last name"
        C1TreeView1.Columns.Add(column)

        ' DataSourceの設定
        C1TreeView1.BindingInfo.KeyField = "ID"
        C1TreeView1.BindingInfo.ParentKeyField = "ChiefID"
        C1TreeView1.BindingInfo.DataSource = EmployeesSelfRefDataSet.GetData()
    End Sub

    Private Sub C1TreeView1_ApplyNodeStyles(sender As Object, e As C1TreeViewNodeStylesEventArgs) Handles C1TreeView1.ApplyNodeStyles
        ' e.Node.GetValueはノードのデータソースを戻します（バウンドモードの場合）
        Dim dataRow = TryCast(e.Node.GetValue(), DataRow)

        ' 指定したノードの行全体のスタイルを変更
        If dataRow.Field(Of Integer)("Id") = 1 Then
            e.NodeStyles.[Default].ForeColor = Color.Yellow
            e.NodeStyles.[Default].BackColor = Color.DarkGreen
        ElseIf dataRow.Field(Of Integer)("Id") = 2 Then
            e.NodeStyles.[Default].ForeColor = Color.White
            e.NodeStyles.[Default].BackColor = Color.DarkBlue
        End If
    End Sub
End Class

' データセットの作成
Public Class EmployeesSelfRefDataSet
    Public Shared Function GetData() As DataSet
        Dim dataSet = New DataSet()
        Dim employees = New DataTable("Employees")
        employees.Columns.Add("ID", Type.[GetType]("System.Int32"))
        employees.Columns.Add("ChiefID", Type.[GetType]("System.Int32"))
        employees.Columns.Add("FirstName", Type.[GetType]("System.String"))
        employees.Columns.Add("LastName", Type.[GetType]("System.String"))
        employees.Columns.Add("Post", Type.[GetType]("System.String"))
        employees.Rows.Add(New Object(4) {1, -1, "John", "Doe", "Director of sales"})
        employees.Rows.Add(New Object(4) {10, 1, "Alex", "Red", "Manager"})
        employees.Rows.Add(New Object(4) {11, 1, "Elena", "White", "Manager"})
        employees.Rows.Add(New Object(4) {12, 1, "Eric", "Green", "Manager"})
        employees.Rows.Add(New Object(4) {13, 1, "Sara", "Blue", "Manager"})
        employees.Rows.Add(New Object(4) {2, -1, "Mary", "Sue", "Marketing director"})
        employees.Rows.Add(New Object(4) {20, 2, "Natalie", "Ming", "Manager"})
        employees.Rows.Add(New Object(4) {21, 2, "Joseph", "Anderson", "Manager"})
        employees.Rows.Add(New Object(4) {22, 2, "Olivia", "Helt", "Manager"})
        employees.Rows.Add(New Object(4) {23, 2, "Samantha", "Silver", "Manager"})
        dataSet.Tables.Add(employees)
        Return dataSet
    End Function
End Class

◎サンプルコード（C#）

using C1.Win.TreeView;

namespace TreeView_ConfigureEditing
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();

            c1TreeView1.Columns.Clear();
            c1TreeView1.BindingInfo.DataSource = null;

            // ツリーの設定
            c1TreeView1.BindingInfo.DataMember = "Employees";
            var column = new C1TreeColumn();
            column.DisplayFieldName = "Post";
            column.HeaderText = "Post";
            c1TreeView1.Columns.Add(column);
            column = new C1TreeColumn();
            column.DisplayFieldName = "FirstName";
            column.HeaderText = "First name";
            c1TreeView1.Columns.Add(column);
            column = new C1TreeColumn();
            column.DisplayFieldName = "LastName";
            column.HeaderText = "Last name";
            c1TreeView1.Columns.Add(column);

            // DataSourceの設定
            c1TreeView1.BindingInfo.KeyField = "ID";
            c1TreeView1.BindingInfo.ParentKeyField = "ChiefID";
            c1TreeView1.BindingInfo.DataSource = EmployeesSelfRefDataSet.GetData();
        }

        // ノード全体のスタイルをカスタマイズ
        private void c1TreeView1_ApplyNodeStyles(object sender, C1TreeViewNodeStylesEventArgs e)
        {
            // e.Node.GetValueはノードのデータソースを戻します（バウンドモードの場合）
            var dataRow = e.Node.GetValue() as DataRow;

            // 指定したノードの行全体のスタイルを変更
            if (dataRow.Field("Id") == 1)  //1行目の親ノード
            {
                e.NodeStyles.Default.ForeColor = Color.Yellow;
                e.NodeStyles.Default.BackColor = Color.DarkGreen;
            }
            else if (dataRow.Field("Id") == 2)  //2行目の親ノード
            {
                e.NodeStyles.Default.ForeColor = Color.White;
                e.NodeStyles.Default.BackColor = Color.DarkBlue;
            }
        }
    }
}

// データセットの作成
namespace TreeView_ConfigureEditing
{
    public class EmployeesSelfRefDataSet
    {
        public static DataSet GetData()
        {
            var dataSet = new DataSet();
            var employees = new DataTable("Employees");

            employees.Columns.Add("ID", Type.GetType("System.Int32"));
            employees.Columns.Add("ChiefID", Type.GetType("System.Int32"));
            employees.Columns.Add("FirstName", Type.GetType("System.String"));
            employees.Columns.Add("LastName", Type.GetType("System.String"));
            employees.Columns.Add("Post", Type.GetType("System.String"));

            employees.Rows.Add(new object[5] { 1, -1, "John", "Doe", "Director of sales" });
            employees.Rows.Add(new object[5] { 10, 1, "Alex", "Red", "Manager" });
            employees.Rows.Add(new object[5] { 11, 1, "Elena", "White", "Manager" });
            employees.Rows.Add(new object[5] { 12, 1, "Eric", "Green", "Manager" });
            employees.Rows.Add(new object[5] { 13, 1, "Sara", "Blue", "Manager" });

            employees.Rows.Add(new object[5] { 2, -1, "Mary", "Sue", "Marketing director" });
            employees.Rows.Add(new object[5] { 20, 2, "Natalie", "Ming", "Manager" });
            employees.Rows.Add(new object[5] { 21, 2, "Joseph", "Anderson", "Manager" });
            employees.Rows.Add(new object[5] { 22, 2, "Olivia", "Helt", "Manager" });
            employees.Rows.Add(new object[5] { 23, 2, "Samantha", "Silver", "Manager" });

            dataSet.Tables.Add(employees);
            return dataSet;
        }
    }
}