I read the stories on your site quite often and do most of this while at work. I work nights and do this out of my car. I have the brightness set quite low so as to not mess with my night vision. I experimented with all three, and personally, think the white font works best ( at least for my application). Under normal viewing conditions any of the three would be fine, but my reading at lowest brightness settings on the monitor, the yellow fonts became hard to read after a few minutes. My example is probably unusual for most visitors to the site, but just wanted to give you my feed back.
Great stories on the site, by the way.