Changing the color of the title bar in WinForm

I created a C# class using @Jonas Kohls answer from here

The class works like a charm and makes it easy to work with multiple forms just call DarkTitleBarClass.UseImmersiveDarkMode(Handle, true); in your load method.

I used this when upgrading some old WinForms apps so its WinForm friendly but only tested on win 8,10 and 11

Example image below Winforms .NetCore 6.0

using System.Runtime.InteropServices;

namespace Myapp.Classes
{
internal class DarkTitleBarClass
{
    [DllImport("dwmapi.dll")]
    private static extern int DwmSetWindowAttribute(IntPtr hwnd, int attr, 
    ref int attrValue, int attrSize);

    private const int DWMWA_USE_IMMERSIVE_DARK_MODE_BEFORE_20H1 = 19;
    private const int DWMWA_USE_IMMERSIVE_DARK_MODE = 20;

    internal static bool UseImmersiveDarkMode(IntPtr handle, bool enabled)
    {
        if (IsWindows10OrGreater(17763))
        {
            var attribute = DWMWA_USE_IMMERSIVE_DARK_MODE_BEFORE_20H1;
            if (IsWindows10OrGreater(18985))
            {
                attribute = DWMWA_USE_IMMERSIVE_DARK_MODE;
            }

            int useImmersiveDarkMode = enabled ? 1 : 0;
            return DwmSetWindowAttribute(handle, attribute, ref useImmersiveDarkMode, sizeof(int)) == 0;
        }

        return false;
    }

    private static bool IsWindows10OrGreater(int build = -1)
    {
        return Environment.OSVersion.Version.Major >= 10 && Environment.OSVersion.Version.Build >= build;
    }
  }
}

[EDIT] Don't forget to add a app.manifest and uncomment the appropriate supported OS.

I solved this problem. This is the code:

[DllImport("User32.dll", CharSet = CharSet.Auto)]
public static extern int ReleaseDC(IntPtr hWnd, IntPtr hDC);

[DllImport("User32.dll")]
private static extern IntPtr GetWindowDC(IntPtr hWnd);

protected override void WndProc(ref Message m)
{
    base.WndProc(ref m);
    const int WM_NCPAINT = 0x85;
    if (m.Msg == WM_NCPAINT)
    {
        IntPtr hdc = GetWindowDC(m.HWnd);
        if ((int)hdc != 0)
        {
            Graphics g = Graphics.FromHdc(hdc);
            g.FillRectangle(Brushes.Green, new Rectangle(0, 0, 4800, 23));
            g.Flush();
            ReleaseDC(m.HWnd, hdc);
        }
    }
}

What you can do is set the FormBorderStyle property to None and do what ever you want with the form using GDI.