#include <GUIConstants.au3>

$hGUI = GUICreate("Test-GUI",300,300)
$hLabel = GUICtrlCreateLabel("",50,50,200,200)
GUICtrlSetBkColor($hLabel,0xFF0000)

GUISetState()

While 1
    $aMsg = GUIGetMsg(1)
    Switch $aMsg[0]
        Case -3
            Exit
        Case $GUI_EVENT_PRIMARYDOWN
            $aCursor = GUIGetCursorInfo()
            If $aCursor[4] = $hLabel Then GUICtrlSetBkColor($hLabel,0x0000FF)
        Case $GUI_EVENT_PRIMARYUP
            $aCursor = GUIGetCursorInfo()
            If $aCursor[4] = $hLabel Then GUICtrlSetBkColor($hLabel,0xFF0000)
    EndSwitch
WEnd