The problem is you're more than like going to get more than one pixel that contains that color.... Like the windows task bar is the same color grey so if you match it then you will match all of the bottom pixels on your display. Anyway, to move your cursor to the first located pixel.
For Each ctrl As Control In Me.Controls("pnlMainPanel").Controls
If ctrl.GetType Is GetType(System.Windows.Forms.Panel) Then
For Each subCtrl As Control In ctrl.Controls
If subCtrl.GetType Is GetType(System.Windows.Forms.TextBox) Then
If subCtrl.GetType Is ...