So we have black hair with green, yellow, blue and turquoise strands, and dark brown hair with red, purple, green, and yellow. I enjoy having assorted brightly-coloured extensions added from time to time in my own RL hair, and thought this style would look nice with colourful clip-on extensions. To continue in the next pic, we have blue, turquoise, and two natural colours with multicoloured ponytail braids. In the pic below, first we have the Maxis colours auburn, brown, golden blonde, black, orange, dark brown, red, platinum blonde, and dirty blond, followed by my additions of grey, white, and green:
I've packaged them with the default natural EA/Maxis colours that came with the child version, plus seven additional colours of my own making. They are for both genders, from Teen to Elder.
Here's a conversion of the TS4 base game female children's 'Braided Ponytail' mesh, rescaled and reshaped to fit adult heads. Before using this hair, be sure your game is patched up to date, as EA fixed the hair-crashing bug in a recent update and if you're not patched up to date you may have problems.