This is an interesting idea. If you wear a dark coat it will absorb heat, but if it is well insulated, little of the heat will get inside to the wearer. It might be possible to design some method of moving the heat to the inside.

The idea of using clothing wired with resistors to keep warm has been around for a long time, at least 40 years. The problem is that when the devices fail it's seemingly at the worst possible time. The time honored system of using dark, layered, well insulated clothing th stay warm is the best bet. Any bets on using solar to stay warm is predicated on the assumption that the sun will be out (and high enough in the sky) when you are out in the cold. Around here that isn't often the case. Plan ahead.

As to staying cool. . .Light colored, loose, lightweight clothing is again better than relying on some battery powered device (whatever it may be). I find linen and silk are nearly transparent to the slightest breeze. Perfect for staying comfortable when walking 18 holes. . .

If anything, it would have to be passive.

Anything active would require too much mechanics/electrics/plumbing to be practical, not to mention the size of the solar panel to support it.