Yes, I do have Lithodora zahnii growing at our Greek house, quite a few plants on a near-vertical natural rock face, facing south. Here are pictures of five, taken in various years between January and March. With us flowering starts in November and goes on into April, but is usually at its peak in January and February. Individual plants remain in flower for many weeks.
The middle picture shows one that I planted a Cyclamen hederifolium under - the cyclamen enjoys the dense shade for its tuber and has no trouble pushing its leaves through on stems around a foot long.
John's remark about different clones having different flower colours: that squares up with what Kit Tan says in her superb book on the endemic plants of the Peloponnese. However, although some clones definitely have the potential to be a deeper blue than others, over the years I have begun to conclude that the flower colour can vary between near-white through blue to pink within each individual plant, depending on age of flower and on weather variations. So although a clone that is naturally pale will never produce darker flowers, a clone that is naturally more blue (as most are, in the wild) can vary from deepish blue to near-white or pink.