Does RAM choice affect power draw and temperature? If so, which is best to use, for a passive mini itx system?

The power draw of RAM is negligible, but if you want the lowest power draw choose low voltage RAM.

Kingston have a selection of HyperX "LoVo" memory that runs at low voltage, DDR3 1600 @ 1.35v and in case of 2x2GB kit DDR3 1333 @ 1.25v. Pricing seems competative to "normal" DDR3 and they have green heatsinks, that I think look rather nice. Not sure they'd "go" with my motherboard colours and of course each to their own!
Regards, Seb

In a few watts range. I'd say not worth it.

DDR3 1.5v is fine. DDR4 will be your next stop

Ok, the power saving is negligible, but what about temperatures?

EDIT: according to this benchmark the range for temperatures is a bit higher, but they are still close to normal voltages...