Traffic in the park slows down somewhat by that time of the year... essentially the park is comprised of three different ecosystems, and they all have their own beauty. MOST of the visitors to the park use the Hwy 60 route, but (maybe I shouldn't mention it!) there is another access into the park from the northeast side off Achray Road, near Pembroke. There are some beautiful sights up there, like Barron's Canyon, and you're less likely to meet others...
Mike.
P.S. While you may go looking for colours, be open to what you see instead! When I was working on moose research in the park in 1983 I went out for a day with two other photographers - Bill Reynolds (who wrote a book on Algonquin) and a German woman from Toronto. We went out to shoot pictures of moose, and, surprise, surprise, didn't see a one, so we took macro shots of the lichens and things instead.