The dorsal sepal is completely normal in appearance, both shape and coloring, as is the whole flower. Perfectly flat symmetrical dorsals are sometimes seen in hybrids with generations of selective breeding behind them, but far more rarely in species. In either case it can be quite variable season to season or even flower to flower. With this species you can see a new flower ever few weeks for quite a while. Each will be a bit different and some may approach perfect symmetry.