I have been looking for three years for a product like this! Lancome used to make a powder eyeliner with an applicator such as this one. The powder is actually inside and as you use the applicator, it comes out little by little. Mine lasted for over a year! I saved it as an example but it looks like someone else picked up on their idea.
This product is called Anastasia Brow Filler and I got mine at Ulta (Sephora carries it too). It costs $18-20 and has two sides. The filler offers blonde on one end and brunette on the other. The unique formula comes out slightly damp so it can adhere to the skin. I hope they carry this product in an eyeliner soon and use blues and greens. I would buy one in every color.
This product is actually for your brows but I used it as an eyeliner and it worked great. I used the darker side under my eyes and then the lighter color on my brows. It worked effectively and I was quite pleased with the results. The darker shade is not very dark though, but you could use it as a base for another eyeliner. I actually tried this today with the lighter color. I used a small amount as a base and then added a little of my L'Oreal Hip pigment stick and it turned out really nice. Not too dark for the daytime either. After all, who wants to show up at preschool and be the mom decked out in dark makeup? "It's not a fashion show", as my mom would always say.