I have received these plants hardy to zone 6b, minimum temperatures of -23°C (-9.4°F). I know there are numerous species of Sempervivum that look alike, but I kind of hope somebody knows some details about them. Their diameter is 2-9 cm (0.8-3.5 inches) and were collected from a garden with the approx. coordinates 46°N, 23°E, elevation 400 m (1300 ft).
The leaves are green. In reality the leaves don't have the white shine that appears in this photo.