Looks like that paint to me as it's worn off the bolt handle and other parts such as the trigger and rear of the guard to illustrate the difference. But I could be wrong!
And Dangles, yes. Painting was a wartine expedient to the usual 'browning' or 'blacking' which were an early form of hard wearing corrosion protection. But it was neither hard wearing or corrosion protection because it was nothing other than a form of controlled corrosion for want of a better term.
Where did you get the photo of the Owen BAR? That's ours from Warminster!!!!!