In summer 1999, Manja Kolb watched a complete rainbow between Riesa and Leipzig, which was intersected by a coloured arc in its upper part. It was as bright as the rainbow, but its colours were less intensive. At the point where it intersected the rainbow, it was significantly thicker.
This is not the only observation of that kind. The book "Rare Halos, Mirages, Anormalous Rainbows and Related EM Phenomena" by Coroliss contains several descriptions of rainbows which are laterally displaced and intersect. There are no feasible explanations for that phenomenon up to now. But there are no doubts that it is real.