I just got this today and tried it out this morning. Wow. It did exactly what I hoped it would. It covered the gray, and just with a few swipes. I applied it just like I would mascara, and it acted the same - yes, it's wet, then dries (like mascara). If you apply it too liberally, it will glop (just like mascara). If you wet it, it will wash off (just like mascara). No surprises folks!
I did use it this morning to touch up my grey roots before exercising. I pull my hair back in a head band, and the roots show notably. This covered it up in seconds, and was easily applied without pulling the hair out of the band. Wonderful! I worked out for over an hour and sweated. It didn't run down on to my forehead, but it did get "wet" again, so that if I touched the hair at the roots I could see brown on my finger tips. However, it stayed in place and was not noticable. I showered after working out, dried my hair, reapplied the touch up hair mascara (I carry it in my makeup bag with the lash mascara) let it dry for a few seconds and sprayed my hair. No fuss. No problem. No gray. Yeah!
I just ordered another one in the same color (warm brown). I think this will extend my time between touch ups considerably (I hope, cause it's crazy expensive to touch up roots)! This is what my hair stylist/color specialist recommended using btw treatments. He didn't recommend a certain brand, but rather the mascara type touch-up product itself. This was exactly what I anticipated and hoped it would. Granted, it's my first day using it, but if my opinion changes, I'll post an addendum. Oh, saw the same product for less on amazon, but the S&H made it more than this one. So far, this seems to be the best value. Haven't seen it in stores, so if someone finds it for less, leave a comment and let me know!
Hope this helped!