I read the thread for trombe walls and thought it might be good to talk about a related concept. Thermal mass flooring can help to both absorb the excess heat gain from the sun during the day as well as radiate heat at night when the sun isn't around to provide.

The concept is similar to a trombe wall except that its is of course a floor. The materials need to be both absorbent (UV and heat energies as well as massive enough to retain and dissipate that energy.

I have a large concrete slab along the southern side of my home and it is colored a dark grey (could have gone black but then you wouldn't be able to walk on it during the hot summer days). It is comfortable to walk on and only cold during the winters. If I had to do it again, I would install a radiant flooring system in it to handle the months when I don't get as much solar heating and harsher nighttime temps.

NJ, during overcast days in the winter, do you have troubles with cold floors. I would assume without some kind of back up, you run into some periodic comfort issues. Also, how are you handling the summer sun and heat gain that can.... well burn your feet if you aren't careful.