As I understand it, both. One of the colored wires is the 12v positive, the
other one is the 5V positive. The blacks are the ground for each one. I'm
not sure if there's any standards regarding color, but I'm sure that there
is regarding the position. A quick search for "molex 12v 5v" turns up a
number of interesting links, including
http://www.heatsink-guide.com/psplug.htm, indicating you can get 12v, 5v, or
the difference between the two, 7v. Not sure I'd play around with that on
my $200 video card, though.
Clint