I don't know about font preference, but, in theory the color yellow enhances concentration and captures attention - so its use, aside from the obvious contrast, could just be used to capture a person's attention and make them focus on something. It's the same reason the color yellow is dominantly used for legal pads, post it notes, caution signs/tape, the Yellow Pages (being essentially a giant book of ads), #2 pencils, etc. There's also the theory that a yellow background with a black font is the easiest to read.
Probably not super useful info, but food for thought.