I can confirm that the colour of the Beech AT-11 Kansan ZK-AHO on 30-01-1973 was indeed white with red trim. http://nzcivair.blogspot.com/2010/06/mention-of-piet-van-asch-in-blog-on-zk.html
And re triple glider tows on http://nzcivair.blogspot.com/2010/06/triple-tow.html
I managed to dig up an even earlier photo of a triple glider tow.
This fantastic monochrome shot shows the Piper Cub ZK-BNS towing three gliders out of Invercargill Airport in March of 1968.