what is the shelf life of the product. Also I am not use to coloring my own hair and need advice. I plan on coloring a portion of my hair in the front that is gray. In the past I had it highlighted using your color. I need to catch more gray, so I will color the portion of gray. I then want to highlight it with the same color using a cap. I know to mix eqal part of the color and developer which will be a small amount to color the gray. I guess my question is how log does the developer last so I can highlight the rest of my hair after coloring the gray. Do I need to purchase and additonal hair kit. I just wasn't sure if I open the developer, how long i have until it goes bad
