I have a white mesh jacket that was hot -- but not unbearably so -- in 90 degree heat the other day. There are also lots of options for mesh or ventilated gloves. Lighter colors are going to be better heat-wise, but they'll also be worse from a showing-grease standpoint.
I think the real problem with summer motorcycle gear is that it's designed for people on motorcycles. As in, they go faster than 30-40mph. They don't break down and have to push their motorcycles. They don't pedal off the line/up hills. They don't have to run up and down the street to get their motorcycles started. Barring the few of us who have fast mopeds that always work and are easy to start, we have a lot less airflow and get a lot more exercise than most motorcyclists, so any gear we get, no matter how lightweight or ventilated it is, is still going to suck. It's up to you whether you want to wear the gear and be guaranteed to sweat like mad all the time, or ditch the gear, be slightly cooler, and potentially deal with more road rash/broken bones if you crash.