Thanks but you are correct in that I want something automated.
I have done it manually with Photoshop about 20 years ago.
Being of a slightly careful person with cash, I photographed my whole wedding back in 1976 with a 35mm camera and TLR loaded with monochrome film together with my Super8 cine camera. For the group shots I used a tripod and delayed action.
All this amused (?) the guests.
Anyway around 20 years ago a visitor commented on a photo of the happy couple with parents, saying it must have been a long time ago (because of lack of colour!)
This spurred me on and very painstakingly, using colour photos guests had taken, I hand coloured said photo, printed it and placed it on display.
However, I was not tempted to do the same with several hundred other photos.
The app I mentioned originally can do a magnificent job in around 10 seconds and can work its way automatically through a folder of pictures.
Sometimes the results are brilliant but on other occasions you get colour aberrations, which can be reduced manually but rather defeat the object.