I tend toward black bags as I wear a lot of black (or at least black background) clothes, so my bags aren't seasonal. That said, I have a black Kooba Paige that I'm waiting for dryer weather to start using.
I haven't used my Denim Speedy over the last weeks as the weather here in Germany is pretty bad at the moment. And I finally took my Hudson PM out of the dustbag But most of my bags I use all year, so I don't really switch.
We usually can squeeze out a little bit more of summer in September in the Seattle area.
In general, most of my bags I can use year 'round. But those that are pretty summery (Felix Rey straw tote, a cream canvas bcbg and a cute kelly green Juicy) are going to get put away in a few weeks.
I have a black patent Prada shopper than I can't WAIT to bring out again for F/W.