It’s a good explanation of how hex colour codes work, but in this day and age it's so much simpler to use (and think in) rgb(n, n, n) notation. Not to mention the hsl(n, n%, n%) notation that is supported by modern browsers.
I exclusively use HSL notation because if you're using less functions like spin(), [de]saturate() and [lighten|darken]() it's what makes the most sense.
I've started using HSL too. Paul Irish is right, once you start using it, it's really easy to grasp and use on the fly.