The following script lets me display text against a transparent background.
#AutoIt3Wrapper_Au3Check_Parameters=-d -w 1 -w 2 -w 3 -w 4 -w 5 -w 6
#include <GUIConstantsEx.au3>
#include <WinAPI.au3>
#include <WindowsConstants.au3>
Global $hGui = GUICreate("", 400, 300, -1, -1, $WS_POPUP, BitOR($WS_EX_TOPMOST, $WS_EX_LAYERED))
GUISetBkColor(0xF1F1F1)
Global $sString = "Testing 123" & @CRLF & "I've got info for you."