Chairman of Monarchy New Zealand, Sean Palmer, told the Herald Online the tribute shows New Zealand's strong connection to the monarchy.
"This baby is going to grow up to be the king or queen of New Zealand one day and we think it's nice to mark the start of this person's life," he said.
Most of the structures are already fitted out with the appropriate gear, so the cost of illuminating in either pink or blue won't be that great.
And, Mr Palmer pointed out, the project has gained global interest, shining a spotlight on NZ. The Kiwi idea has already been adopted in Canada, where the National Tower in Toronto and the Niagra Falls will be lit up.
While baby guessing games are buzzing, Mr Palmer said he's secretly planning for a late arrival of a baby girl, hopefully called Elizabeth.
"I think it would be very nice after 61 years of Queen Elizabeth II - and we will have some some years with King Charles and King William - I think it might be nice to have a queen again.
"If I had to guess, I think it would certainly be a great gesture to be looking at an Elizabeth III."
More on the royal baby:
Check out Kate's growing baby bump here
Reflect on the royal romance in this interactive timeline
Click around the map or have a search to find out all the landmarks that will be lit up:
- www.nzherald.co.nz