R – change hue/saturation of screen without using form background color

As per Prerak K's update comment (since deleted):

I guess I have not presented the question properly.

Situation is this: I want to load data into a global variable based on the value of a control. I don't want to change the value of a control from the child thread. I'm not going to do it ever from a child thread.

So only accessing the value so that corresponding data can be fetched from the database.

The solution you want then should look like:

UserContrl1_LOadDataMethod()
{
    string name = "";
    if(textbox1.InvokeRequired)
    {
        textbox1.Invoke(new MethodInvoker(delegate { name = textbox1.text; }));
    }
    if(name == "MyName")
    {
        // do whatever
    }
}

Do your serious processing in the separate thread before you attempt to switch back to the control's thread. For example:

UserContrl1_LOadDataMethod()
{
    if(textbox1.text=="MyName") //<<======Now it wont give exception**
    {
        //Load data correspondin to "MyName"
        //Populate a globale variable List<string> which will be
        //bound to grid at some later stage
        if(InvokeRequired)
        {
            // after we've done all the processing, 
            this.Invoke(new MethodInvoker(delegate {
                // load the control with the appropriate data
            }));
            return;
        }
    }
}

Using the HSVtoRGB procedure found here, you can hook both your TrackBar controls to the same event handler and use this code:

Private Sub tbHUE_Scroll(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles tbHUE.Scroll, tbSaturation.Scroll
  Dim r, g, b As Integer
  HSVtoRGB(r, g, b, tbHUE.Value, tbSaturation.Value / 50, 255)
  BackColor = Color.FromArgb(r, g, b)
End Sub

Edit: Here is the corrected procedure since the one in the link doesn't really follow best practices:

Private Sub HSVtoRGB(ByRef Red As Integer, ByRef Green As Integer, ByRef Blue As Integer, ByVal Hue As Double, ByVal Sat As Double, ByVal Value As Integer)
  Dim i As Integer
  Dim f As Double, p As Double, q As Double, t As Double

  If Sat = 0 Then
    Red = Value
    Green = Value
    Blue = Value
    Exit Sub
  End If

  i = CInt(Hue) \ 60
  Hue = Hue / 60
  f = Hue - i
  p = Value * (1 - Sat)
  q = Value * (1 - Sat * f)
  t = Value * (1 - Sat * (1 - f))

  Select Case i
    Case 0
      Red = Value
      Green = CInt(t)
      Blue = CInt(p)
    Case 1
      Red = CInt(q)
      Green = Value
      Blue = CInt(p)
    Case 2
      Red = CInt(p)
      Green = Value
      Blue = CInt(t)
    Case 3
      Red = CInt(p)
      Green = CInt(q)
      Blue = Value
    Case 4
      Red = CInt(t)
      Green = CInt(p)
      Blue = Value
    Case 5
      Red = Value
      Green = CInt(p)
      Blue = CInt(q)
  End Select
End Sub