To paint hair with acrylic paint, start by sketching out the general shape of the hairstyle you want to paint. Once you have the outline of the hair, use a small brush to fill in the individual strands of hair. To add dimension and realism to your painting, use a variety of colors and shades of acrylic paint. For example, use light colors for highlights and darker colors for shadows. Finally, use a fine-tip brush to add any final details, such as flyaway hairs or split ends.