I use Clairol Natural Instincts (Creme)...it's kind of in an orangey/brown box with green writing...and lasts at least 28 shampoos. I also have dark brown hair and the same wirey grey hairs you speak of....I choose a redder shade called Darker Auburn (but its not THAT dark, even on the model on the box), since I would like redder tones in my hair, but have found the color true to my expectation. You can find tones that are brown in nature only, I do believe. It does rinse out gradually, and it seems rather hard to notice that it's washing away. I need to redo mine but am just being lazy about it.

I also pluck the shorter grey hairs, they tend to stick up and out and drive me nuts.