Hairdo Highlight Extension 18" Human Hair Color Shown: R14/25 100% Human Hair. Never a dull moment thanks to this color-rich, clip-in extension! With 18 glossy inches of gently cascading human hair and your choice of 12 gorgeous shades, the Hairdo 18" Human Hair Highlight Extension is the perfect way to add instant highlights or lowlights without making the commitment to color your own hair! Available in 12 multi-tonal shades.