How do you paint Beats by Dr. Dre yourself?

I bought a pair of white beats a few days ago and i kind of wanted to add about 2cm of light blue around the top edge of the headband, but i wasn't really sure what to do. I was planning on just buying painters tape, rustOleum plastic spray and doing it like that, but after researching into it a bit more i realized I might need to do more than just that. Do i have to add a primer and then the blue rustOleum with a gloss or sandpaper it and then do that? I really just need help with what ever you have to offer, whether it be what type of paint or how to prepare the plastic or how it should be done, please tell me.