I have a black paint v1 Summilux. I like it a lot, but flare resistant is not what I would call it. The main lens flare tests that I use to assess a lens for my use are photos with:
- point sources of bright light near but inside the edge of the frame
- point sources just outside the frame but shining on the front element
- a large bright area like that window you showed above, but just outside the frame, with a dark subject and low-key photo
- a photo of a bird on a wire or squirrel or similar on a branch against a bright sky
The f1 Noctilux was by far the best on film. Everything fails some test or another on digital, at least everything I have tried so far. It is very interesting how many great lenses fail test 3. The Leica ASPH lenses mostly do badly, even stopped down a bit, and even the Summicron-R 35mm, which is a very flare resistant lens, fails it badly, despite not flaring when you point it at the sun or a stage light. I may be able to figure out why, but I find what a lens does is more important for my photography, particularly when design and construction are not things I can change.
The colour of the coating is often not indicative of its composition; it is mostly indicative of its thickness, and for multi-coating, which wavelengths are least well controlled for reflection. It can also change with a <1% alteration in composition, including of contaminant compounds that are still within spec.
There is a good description of the basics of coating here:
Camera Lens Anti-Reflection Coatings: Magic Explained