I haven't used redwood myself, but other builders here have and will probably recommend it. Redwood is slightly heavier and slightly stronger than most cedars. A boat built of all redwood would weigh only about 1# more than an all-cedar one. If you like perusing technical data, you can check out some wood properties courtesy of the US forest products lab:

http://www.fpl.fs.fed.us/documnts/FPLGTR/fplgtr113/fplgtr113.htm

I've read that redwood has a tendency to darken with sun exposure and/or age, so expect your kayak to darken over time.

Another thought: Scratches on the hull show up light, whether it's just a scrape/rub in the varnish or stressing of the fiberglass cloth. The lighter the hull, the less scratches show. (this is why most productions kayaks have white hulls, too)

Dean