I have a black IS250, and noticed swirls quite soon after collecting. That was in my old regime of ... hose it down, wash with sponge, rinse and chammy dry.
Have now seen the error of my ways.....new regime
Hose down.
Attach soft brush to hose and clean with top down strokes making sure no grit stays on the brush.
Meguiars wash mit with Nxt generation wash solution and bucket of water to rinse the mit off.
Dry off with microfibre.
Also used some Zymol cleaner wax which removed most of the swirls I (or dealer ?) had put on the car.
Must say too, that there's nothing that shines quite like her when I'm finished ! Roll on the summer.