Originally Posted by gap

Probably the most logical configuration, and in accordance with the steady green light recorded for La Plate in 1911.
My one doubt is about the unusually dark shade of grey representing the lighthouse in the historical picture you have pointed me to. Human eye's spectral gamma and the one of B/W films are quite different. Usually, red shades look much darker on old B/W photographs than they would have looked to the nake eye, and conversely green shades are recorded as ligh grey, much lighter than the eye perceives them. This is especially true for old films and orthocromatic emulsions.
Going by the tone of grey seen on your picture, we should conclude that the lighthouse was painted red rather than green; nonetheless the picture might have been taken with a panchromatic film which is proportionally lesser sensitive to green than to red, and/or the green paint used on La Plate might have been unusually dark. The tower beeing photographed on the background of the brighter ocean surface, might also have enhanced the darkness of the tower, making it to appear as a silhouette...