I show how I created this image, using a very simple process, in iColorama-S on the iPhone. The face itself is simply a pixelation of a chosen image. You could easily make many variations on this process using different images and pixelations.
I started with this photo of one of my Gelli prints. I chose it for its colors, which resemble skin tones. You could start with almost any image.
I used a preset under Effect/Pixels to pixelate the image. I tried many presets and slider settings. I liked this particular one because it has some dimensionality to it.
I used Brush/Paint and selected a yellow color from the image, and I painted over the white background to make a face shape. Then I continued using Brush/Paint to draw some lines, using the smallest brush size setting.
I continued using Brush/Paint and selected a red color from the image, and I painted her shirt.
I continued using Brush/Paint and I painted some lines for her hair and outlines of her face and figure, using various colors and a very small brush.