[DXCategory("Events")]
public event BarItemCustomDrawEventHandler CustomDrawItem

<DXCategory("Events")>
Public Event CustomDrawItem As BarItemCustomDrawEventHandler

using System.Drawing;
using DevExpress.XtraBars;

namespace FlyoutExample {
    public partial class XtraForm1 : DevExpress.XtraEditors.XtraForm {

        BarButtonItem lastClickedButton;

        public XtraForm1()
        {
            InitializeComponent();
            barManager1.CustomDrawItem += barManager1_CustomDrawItem;
            barButtonItem1.ItemClick += BarButtonItem1_ItemClick;
            barButtonItem2.ItemClick += BarButtonItem2_ItemClick;
            barButtonItem3.ItemClick += BarButtonItem3_ItemClick;
        }

        private void BarButtonItem1_ItemClick(object sender, DevExpress.XtraBars.ItemClickEventArgs e)
        {
            //...
            lastClickedButton = e.Item as BarButtonItem;
        }

        private void BarButtonItem2_ItemClick(object sender, DevExpress.XtraBars.ItemClickEventArgs e)
        {
            //...
            lastClickedButton = e.Item as BarButtonItem;
        }

        private void BarButtonItem3_ItemClick(object sender, DevExpress.XtraBars.ItemClickEventArgs e)
        {
            //...
            lastClickedButton = e.Item as BarButtonItem;
        }

        private void barManager1_CustomDrawItem(object sender, DevExpress.XtraBars.BarItemCustomDrawEventArgs e)
        {
            if (e.LinkInfo != null && e.LinkInfo.Link.Item == lastClickedButton)
            {
                //apply the default "Pressed" appearance
                e.LinkInfo.LinkState = DevExpress.XtraBars.ViewInfo.BarLinkState.Pressed;
                // or
                //custom draw last pressed buttons
                e.Cache.FillRectangle(Brushes.DarkOrange, e.Bounds);
                e.DrawArrow();
                e.DrawBorder();
                e.DrawCheckBox();
                e.DrawGlyph();
                e.DrawText();
                e.Handled = true;
            }
        }
    }
}

Imports System.Drawing
Imports DevExpress.XtraBars

Namespace FlyoutExample
    Partial Public Class XtraForm1
        Inherits DevExpress.XtraEditors.XtraForm

        Private lastClickedButton As BarButtonItem

        Public Sub New()
            InitializeComponent()
            AddHandler barManager1.CustomDrawItem, AddressOf barManager1_CustomDrawItem
            AddHandler barButtonItem1.ItemClick, AddressOf BarButtonItem1_ItemClick
            AddHandler barButtonItem2.ItemClick, AddressOf BarButtonItem2_ItemClick
            AddHandler barButtonItem3.ItemClick, AddressOf BarButtonItem3_ItemClick
        End Sub

        Private Sub BarButtonItem1_ItemClick(ByVal sender As Object, ByVal e As DevExpress.XtraBars.ItemClickEventArgs)
            '...
            lastClickedButton = TryCast(e.Item, BarButtonItem)
        End Sub

        Private Sub BarButtonItem2_ItemClick(ByVal sender As Object, ByVal e As DevExpress.XtraBars.ItemClickEventArgs)
            '...
            lastClickedButton = TryCast(e.Item, BarButtonItem)
        End Sub

        Private Sub BarButtonItem3_ItemClick(ByVal sender As Object, ByVal e As DevExpress.XtraBars.ItemClickEventArgs)
            '...
            lastClickedButton = TryCast(e.Item, BarButtonItem)
        End Sub

        Private Sub barManager1_CustomDrawItem(ByVal sender As Object, ByVal e As DevExpress.XtraBars.BarItemCustomDrawEventArgs)
            If e.LinkInfo IsNot Nothing AndAlso e.LinkInfo.Link.Item Is lastClickedButton Then
                'apply the default "Pressed" appearance
                e.LinkInfo.LinkState = DevExpress.XtraBars.ViewInfo.BarLinkState.Pressed
                ' or
                'custom draw last pressed buttons
                e.Cache.FillRectangle(Brushes.DarkOrange, e.Bounds)
                e.DrawArrow()
                e.DrawBorder()
                e.DrawCheckBox()
                e.DrawGlyph()
                e.DrawText()
                e.Handled = True
            End If
        End Sub
    End Class
End Namespace