While having towels of the same color looks neat, in reality it's not always that convenient. To keep them distinguishable, I designed a clip with a letter or different color so you always know which towel is yours.

This clip uses two M3x20 bolts and a spring from an old laundry peg. As far as I've tested all the springs are the same no matter the peg, but it's important that the inner diameter is ~3mm and it's about ~14mm long. Assembling the printed parts is not the easiest thing to do, but it is manageable. I printed it with a two shaded silk filament to give each side of the clip a different glossy color.