I have a yellow screen on my Mac mini

Do you mean the entire screen is shades of yellow? If so, the blue channel conked out. It could be a bad video cable, or the monitor itself. Try wiggling the cable a bit on both ends (not hard). If the screen flickers back to normal color, replacing the cable will probably do it.

Did that do it? I sure hope it was just a bad cable, because it could also be a fault with the monitor (not too bad if it wasn't a real expensive one). Or worse, something fried on the integrated graphics hardware in the Mini.

Gotta love cheap fixes. 🙂