I used Soft Pastels by Artists Loft. You can buy them at Michael's. Use a spray bottle and saturate the strand of hair with water. Then grab a soft pastel and run it up and down the strand of hair. The first few times with each pastel takes awhile. Eventually they will wear and develop grooves - then it goes faster. With my dark hair, the bright pink, bright green and bright blue show up the best.
A simple ponytail; could curl the ends for a princess effect or use hair bows and ponytail clasps to make the ponytail appear less simple; could wrap a bit of hair (plaited or not) around the hairband.