Here is an example of more formally painted necks.
chart explaining the different stages of a Geisha's training, and how her makeup application and colors change throughout those stages. (Click on the image to enlarge it.) Notice in the chart how the amount of red in the eye make-up starts to decrease with time from when a maiko becomes a geisha. Eventually the red eye color will be minimal or may even be excluded all together.
discussion forum I read through theorized that red is worn by the younger trainees because the color is considered a color of youth and virginity. This is why so much red adorns a maiko's outfit and then gradually, for the most part, disappears as she advances and becomes a geiko.