Find a cute little jar and an old makeup brush, and you're set. Here's my "recipe":
1 tablespoon baking powder
1 tablespoon cornstarch
some powdered rosemary (not sure why I did this, but it seemed like a good idea; feel free to omit)
Shake it up. Wait a day till your roots are oily. Dip the makeup brush in the powder, apply it to your roots, massage it around a little and then let it sit for a few minutes. Then all you have to do is use a natural bristle hair brush (I use one with wooden bristles because I have enough hair for two people, but a boar bristle brush would work too) to brush it through. Even though my hair is medium to dark brown, it completely disappeared and I'm completely happy with the results! Hooray!
Let me know what you think if you try it!