What kind of black dye should I use to make coon tails on blonde hair?

So tomorrow I'll be planning to buy human hair extensions. I'll be buying Satin Strands Remy I-Tip Malibu (or something like that, I dunno, just checked on the online store but I'll be going to the local store in my town) and I'll be making coontails with the platinum or blonde streaks. I don't care what you say of what I want to do. Anyways, I be wanting to get black hair dye and put stripes on the strands of hair. but, idk where to buy cheap but good hair dye or how to make them without the color running onto an unwanted place. so....yeah, help? xD