Some areas of a painting require many layers of color. I make sure to allow time (at least a few days, but sometimes it can even be weeks) for each layer to dry. If I add too many colors of paint at one time it all starts to blend together into a muddy mess, and you loose the clearness of colors that give my oil paintings their vibrancy.
I did a little more work painting the center of this sunflower.
After adding some highlights to the center, I painted the shadows using dark brown and navy blue.