I'd let logic take the reins here. By that I mean, you tell your son "you can do what you want to your own hair, with these considerations. 1/ you earn the money to buy extra hair stuff beyond shampoo. 2/ you get up early enough to spray or style your own hair without being late for the bus, carpool, or school 3/ there will be no hairspray or gel or goop on any bathroom surfaces, carpets, clothing. 4/ it's not against any school dress code rules.
You explain to him that he's almost a teen. Mom and/or Dad pays for the rent or mortgage, electricity, clothes, food, water, the car, etc. But when pre-teens and teens start deciding they want hair colors, manicures, a cooler backpack than the basic one Mom had in mind, etc, it's time to step up. Make sure to take him to Sally Beauty and show him the cost of hair color spray. That can be a real wake up call.
I remember once when my son and I were shopping for school shoes for him. I found a good pair of sneakers. He was a young teen and he REALLLLLY wanted this particular pair with some sports guy's name on them. There wasn't much difference between what I chose and what he chose except for a small autograph of the guy. I told my son "sure, you have some birthday money, I'll chip in what I was going to pay for the sneakers I chose, and you pay the rest". He was so happy. Until - he turned his choice of sneakers over and saw the price. All of a sudden he turns in Mr. Consumer Guide. He was indignant. "These are practically the same shoes, except these have [sports guy's] name on them, and they're an extra $80 for that!". Lesson learned. He chose the shoes I originally chose.
Make sure your son has a way to earn a little extra money (extra chores beyond the regular chores that go along with being part of the family and the household, neighborhood yard work, etc).
Either your son will do what's necessary to color his hair, or when the logical consequences (time, money, extra cleaning of the bathroom) set in, the desire will phase itself out naturally.