Rainbows are seasonally appropriate for every season! They never go out of style.
I think we are nearing the end of the rain(bow) here in Seattle finally. It's still blustery and still showering here and there but we're getting more and more sunshine and soon it will be GLORIOUS! Have you ever witnessed a Northwest summer? They are kind of the best ever. Just don't tell anyone that, we want to hold onto our inhospitable reputation lest more people try to move here.
It's hard to bring something to a BBQ that people will like that's still simple and quick to throw together. Throwing a few bits to fruit onto a stick is pretty much as simple as it can get. And who doesn't like a rainbow! You can dress up that boring buffet table covered in potato salad and baked beans!