I want to change the colour of my stem and seat clamp, sure a few on here have done it. Anyone got any pics?

No pics to hand, but be careful which pimer you use. If bare metal go for an etch primer. I didn't, but will next time….

I take it that'll help the paint stay on?

To get a finish that looks professional will take a lot of time and effort.

A friend of mine has some professional paint guns, so can use those if need be. But would need some decent paint as well.

Don't know if you've ever been onto weight-weenies, but many on there do some painting, with very good results.