For fear of being eaten alive...I will admit it....I sun in DS. 
It looks very natural. His hair hasn't frazzles, or his eyes fallen out.
He asks; "can I have some blondie spray?" Because he wants to be blond. And I'll spray a bit on every couple of weeks.
I only do it in the summer when his hair is surfer dude style, and he spends a lot of time out side. At the beginning of September, he'll have the back and sides cut, and we won't use sun in. I doesn't wreck his hair, but then he loves to pile lots of my expensive condition on.
But tbh, I don't think it will work so well on the roots. But then DS has had dark roots since he was born. 
And no, he doesn't want a spray tan, so he tells me.
He is very proud of his six pack, though.
It's only his hair, for heavens sake. And yes, I'm, the mother who fusses if the DC drink non organic milk, or consume aspartame.