The veteran broadcaster, 86, travelled to the remote Galapagos Islands this summer for his new Sky series Galapagos 3D.
The species was discovered a few years ago, but it has never before been captured on camera.
Speaking of his delight at the pink iguana, Attenborough said: "It's got great big blotches of pink on it."
He continued: "It's a remarkable thing in this day and age when you think about the number of scientists per square meter in the Galapagos, and yet suddenly we have discovered a new species.
"A little periwinkle or something which nobody has identified before is one thing, but this is more than that, it's a large pink iguana! I used to collect stamps, and this was a Penny Black of the natural world in a very big way."
Galapagos 3D will be broadcast at 7pm tonight (January 1) on Sky 3D. It will also be simulcast at 7pm on Sky1 HD.
Watch Sir David Attenborough talk to Digital Spy about Galapagos 3D below: