C# – Displaying a MessageBox on top of all forms, setting location and/or color

You could use the String.IndexOf Method and pass StringComparison.OrdinalIgnoreCase as the type of search to use:

string title = "STRING";
bool contains = title.IndexOf("string", StringComparison.OrdinalIgnoreCase) >= 0;

Even better is defining a new extension method for string:

public static class StringExtensions
{
    public static bool Contains(this string source, string toCheck, StringComparison comp)
    {
        return source?.IndexOf(toCheck, comp) >= 0;
    }
}

Note, that null propagation ?. is available since C# 6.0 (VS 2015), for older versions use

if (source == null) return false;
return source.IndexOf(toCheck, comp) >= 0;

USAGE:

string title = "STRING";
bool contains = title.Contains("string", StringComparison.OrdinalIgnoreCase);

Try the following approach:

AutoClosingMessageBox.Show("Text", "Caption", 1000);

Where the AutoClosingMessageBox class implemented as following:

public class AutoClosingMessageBox {
    System.Threading.Timer _timeoutTimer;
    string _caption;
    AutoClosingMessageBox(string text, string caption, int timeout) {
        _caption = caption;
        _timeoutTimer = new System.Threading.Timer(OnTimerElapsed,
            null, timeout, System.Threading.Timeout.Infinite);
        using(_timeoutTimer)
            MessageBox.Show(text, caption);
    }
    public static void Show(string text, string caption, int timeout) {
        new AutoClosingMessageBox(text, caption, timeout);
    }
    void OnTimerElapsed(object state) {
        IntPtr mbWnd = FindWindow("#32770", _caption); // lpClassName is #32770 for MessageBox
        if(mbWnd != IntPtr.Zero)
            SendMessage(mbWnd, WM_CLOSE, IntPtr.Zero, IntPtr.Zero);
        _timeoutTimer.Dispose();
    }
    const int WM_CLOSE = 0x0010;
    [System.Runtime.InteropServices.DllImport("user32.dll", SetLastError = true)]
    static extern IntPtr FindWindow(string lpClassName, string lpWindowName);
    [System.Runtime.InteropServices.DllImport("user32.dll", CharSet = System.Runtime.InteropServices.CharSet.Auto)]
    static extern IntPtr SendMessage(IntPtr hWnd, UInt32 Msg, IntPtr wParam, IntPtr lParam);
}

Update: If you want to get the return value of the underlying MessageBox when user selects something before the timeout you can use the following version of this code:

var userResult = AutoClosingMessageBox.Show("Yes or No?", "Caption", 1000, MessageBoxButtons.YesNo);
if(userResult == System.Windows.Forms.DialogResult.Yes) { 
    // do something
}
...
public class AutoClosingMessageBox {
    System.Threading.Timer _timeoutTimer;
    string _caption;
    DialogResult _result;
    DialogResult _timerResult;
    AutoClosingMessageBox(string text, string caption, int timeout, MessageBoxButtons buttons = MessageBoxButtons.OK, DialogResult timerResult = DialogResult.None) {
        _caption = caption;
        _timeoutTimer = new System.Threading.Timer(OnTimerElapsed,
            null, timeout, System.Threading.Timeout.Infinite);
        _timerResult = timerResult;
        using(_timeoutTimer)
            _result = MessageBox.Show(text, caption, buttons);
    }
    public static DialogResult Show(string text, string caption, int timeout, MessageBoxButtons buttons = MessageBoxButtons.OK, DialogResult timerResult = DialogResult.None) {
        return new AutoClosingMessageBox(text, caption, timeout, buttons, timerResult)._result;
    }
    void OnTimerElapsed(object state) {
        IntPtr mbWnd = FindWindow("#32770", _caption); // lpClassName is #32770 for MessageBox
        if(mbWnd != IntPtr.Zero)
            SendMessage(mbWnd, WM_CLOSE, IntPtr.Zero, IntPtr.Zero);
        _timeoutTimer.Dispose();
        _result = _timerResult;
    }
    const int WM_CLOSE = 0x0010;
    [System.Runtime.InteropServices.DllImport("user32.dll", SetLastError = true)]
    static extern IntPtr FindWindow(string lpClassName, string lpWindowName);
    [System.Runtime.InteropServices.DllImport("user32.dll", CharSet = System.Runtime.InteropServices.CharSet.Auto)]
    static extern IntPtr SendMessage(IntPtr hWnd, UInt32 Msg, IntPtr wParam, IntPtr lParam);
}

Yet another Update

I have checked the @Jack's case with YesNo buttons and discovered that the approach with sending the WM_CLOSE message does not work at all.
I will provide a fix in the context of the separate AutoclosingMessageBox library. This library contains redesigned approach and, I believe, can be useful to someone.
It also available via NuGet package:

Install-Package AutoClosingMessageBox

Release Notes (v1.0.0.2):
- New Show(IWin32Owner) API to support most popular scenarios (in the context of #1 );
- New Factory() API to provide full control on MessageBox showing;