Interesting question!
I buy a lot of blue for Brody and pink for Mia, but they have lots of other colors as well...and maybe it's because that's what they sell, too. Mia looks better in darker pinks than lighter pinks, though, so I try to get her darker pinks. I really only try to dress them so their gender is apparent since both have top knots, etc. and when they are together, I would like to distinguish them from each other visually as male and female.
Toys are all colors but I also try to get Brody the blue ones and Mia the pink ones. Brody doesn't care what color, though...he steals Mia's pink ones ASAP!
For other items, I lean more toward generic colors. I haven't found the stroller I want yet, but it will not be pink. It can be pretty much any other color, though.
Very interesting, thoughtful question!