I used to use Great Hair Day but my hair dresser suggested Toppix. It has keratin hair fibers that stick until you shampoo it out. I get the pump top for easier application. You can get it at Amazon, Ulta, CVS, Walgreens and I bet a lot of other places.
If you have just a little to cover, then Great Hair Day is fine, but as I age I needed more coverage and Toppix works.