You should be seeing the added HDR color and contrast difference between the 4K discs and Blu-ray. That's always going to be the most obvious change. For the real resolution difference you'll need to seek out movies and Planet Earth 2 mastered in 4K and captured on 35mm film or digital cameras with at least 3.4K chip.
Here's some reference 4K mastered discs:
Planet Earth 2
Crouching Tiger, Hidden Dragon
The Hunger Games: Catching Fire
Billy Lynn's Long Halftime Walk
Angels and Demons
Star Trek Into the Darkness
also the upcoming La La Land
I doubt he will see any color difference, since the 4 series does not have the DCI P3 filter.