I do that with my wife, without the shampoo.

I hold her hair (BSL) in a ponytail and feed her my cock.

When I'm ready to come, I take my cock our of her mouth and spray my cum on her hair.

To return the favour, I then go down on her and eat her pussy till she has her own orgasm, all the while with my cum still in her hair.

So hot. I love it.