Neither. The lenses were clear glass.
The important part of the glasses were the temples (on the frame), each of which were filled with tiny fuel cells. On the back of each ear was a tiny electrode that charged the battery that was embedded in the back of his skull.
Why, you ask?
X-ray vision takes a lot of effort on the lens optic nerve. Superman needed a pretty good supply of power (in the embedded battery) in order to use X-ray vision for more than a minute at a time, So when he was in his Clark Kent persona, the fuel cells in the physical glasses were actually charging the battery.