The second concern would be about how much the hulls expand and contract due to heat.
I'm not sure that this is too much of a problem. On my Bravo, when I pop the hatch, or open the drain plugs, there is often a huge rush of air due to the expansion of air when the boat sits sealed up in the sun. However the Adventure Island, Revolution, and Oasis kayaks have never had a real problem with expansion or contraction due to heat.
My Bravo is white, the Oasis is yellow, and the other two were red. The Bravo is the worst, but I think that's because the rudder lines, and their tiny holes into the hatch allow the kayak hulls to breath just enough to deal with the issue. After realizing how much pressure can build up in the Bravo, I always loosen the drain plugs on that boat, but I've never worried as much about the kayaks. If it's going to sit in the sun for the day, I'd loosen the plugs or pop a hatch, but if you're in and out of the water for a day, I wouldn't worry too much.
If it were me, I'd buy the color that appeals to you the most.
I've always liked the look of the red boats the best, but the Yellow Oasis that I have now is definitely more visible from a distance than the red ones were. It makes my wife feel safe. Safety is 99% people, and no more than 1% boats, so don't let a bright color fool you into thinking that it's going to keep you safe.
Personally, I like the Dune quite a bit too. It looks more mature, less "toy" and more "boat" to me.