white or coloured font on a black background is never easy on the eyes

personal preference I guess. I like it, and so most of my dev environment is dark themed

I disagree. I go blind looking at bright white backgrounds all day.

It also happens to be an excellent tutorial regardless of colors used.. =)

Yellow on black is the most visible combination of colors.

Is this a preference? I've tried in the past to dig up research actually proving the "most visible combination" through experimentation. I've always assumed that road signs are the combination of colors they are because some empirical research proves it. Never found anything though.

Especially if you're astigmatic.