The color fades quickest from my grey hairs. Unfortunately. Is the texture of your grey hair different than the rest of your hair?
It's the same texture, but all of my hair is curly and frizzy so it might be more porous to begin with? It does tend to take more traditional colors quite well. It's been a half a year since I had my hair done, and except for 6 months worth of roots, the rest of my hair is still holding its color. But that might be different for bright fashion colors, I guess.
The color will show up, but my experience has been that direct dyes fade pretty quickly on hair that hasn't been lightened to increase porosity. If it's something you're willing to keep up at home it could be fun, but be prepared for a less "in your face" look (which it sounds like is what you're looking for).
To be honest, I'm not really even sure what look I'm looking for. Part of me just wants to get through growing out my gray. Right now the roots are driving me crazy and I think it would be fun to try something new that will get me through this phase without giving into the temptation to going back to dying my hair its "natural" color.
Electric_claire, I did henna for years before I started dyeing. From what I understand, you can't combine henna and dye, and I still have several inches of dye left. I might consider it again at some point, but towards the end of my using it, I wasn't really happy with the results I was getting.
ETA: I'll try to get a picture of my hair tomorrow in natural light.