Actually, now that you mention it, yes. I think I'm pretty consistent all through fall, winter and spring, and then in summer, the SECOND it gets hot, everything goes to hell in a handbasket and I wear whatever I can find that is loose-fitting and covers the important parts, regardless of how sloppy it looks. I just can't bring myself to care in the heat. I'm a naturally sweaty person. I can't even stand to have jewellery touching my skin if I'm a bit sweaty, let alone any kind of belt or scarf, which means no accessories all summer (except sunglasses, which I never take off). Then there's the unavoidable sticky gross sunblock, which I have to put not only on my face but everywhere else that's exposed, so I feel like a greased pig at a county fair. And it's a real fight to make myself wear anything other than flip flops. Yep, summer's pretty much my yearly style low point.
I guess it's not so much that my style persona changes -- it's more that I just don't have one in the summer.
Mind you, I have a very casual summer lifestyle. If I had to go work in an office, I'd have to find away to pull it together, and in that case my style persona would probably stay the same. Plus, there would be air conditioning. That would help.