I tend to agree, which supports the theory that the shutter had been lifted but the windrow closed again.
Matthews earliest description of the curtains is plain green. Gerry says the blinds weren't fully closed and at night when no other apartment lights were on weak light did come in from outside.
He recalls having the perception that the
window curtains - green in colour - were drawn closed
He recalls having thought that in that bedroom there was more brightness than there was in his daughter's room (where the external blinds were always fully closed), adding to have had the feeling that that
light was coming from the outside http://www.mccannpjfiles.co.uk/PJ/MATTHEW-OLDFIELD-10MAY.htmHe is certain that, before leaving home the children's bedroom was totally dark, with the window closed, but he does not know it was locked,
the external blinds closed but with some slats open, and the curtains also drawn closed. Asked, he relates
that during the night the artificial light coming in from the outside is very weak, because, without a light being on in the lounge or the kitchen, the visibility inside the bedroom is much reduced.
http://www.mccannpjfiles.co.uk/PJ/GERRY-MCCANN-10MAY.htm