As I keep focusing on mixing colors and filling up more areas, I started feeling the painting is no longer attractive and interesting as it was before. Why? Colorwise, it's supposed to be much closer to the real ones or at least to the reference photo.
I can think of a couple of possible causes of this. I think I started ignoring color changes and transitions in the area I painted with the same mixed color. Before acquiring the skill to mix a proper color, I needed to put thinner layers of different colors again and again over the same area, which unintentionally resulted overlaying effect and inconsistency in color even in a small area. This, I think, was causing unexpectedness of colors and was turning to colors in the favorable way.
Also, I forgot about value changes and didn't pick up darker part carefully.
I guess I need to step back and go back to my instinct to re-inspire myself and finish this piece. Otherwise, this will become one of dullest painting I've ever done.