At 1:58 onwards, he talks about setting up the brush so that the harder you press on your tablet, the darker the colors get, and the lighter you press, the lighter the colors get.

He shows how he set this up by going to the brush settings, then choosing "Pen Pressure" under the "Opacity Jitter" slider.

I did the same but I'm not getting anything like his.
Regardless of whether I press down hard or soft on the tablet, the output is still the same tone.

Do I need to setup other stuff to get this effect? Like opacity or flow?
I'm using Photoshop 7 (shouldn't be a difference) and Intuos 4.
The brush I'm using is the hard round brush.