Painting a plastic

How would you go about doing that??

Obtain paint. Mask the guts. Apply paint.

However, painting doesn’t work very well and comes off very quickly with use. You probably want to dye the plastic. There are several topics explaining how to do that. However, celcon doesn’t dye well, so what yoyo are you wanting to color and what color is it now?

On the other hand, you can get clear yoyos, remove the caps, and paint them on the inside. That normally doesn’t wear off. A number of people do quite nice work in that medium.

Here’s an example by Mr. Higby from the 
The Official: YoYo Showcase! Show off your collection & see others!;topic=3985.0;attach=590;image

Or this fine exdample from this section - 
Buddy Jim’s FHZ!!!

People have also had somewhat better success painting the outside surface with professional grade automotive paints, topped with automotive clearcoat. It’s a bit more durable than the run of the mill hardware store paints.

Yea, but what paints for the car, and for painting the inside?
EDIT: and what would be the best way to paint it like that?

Painting the insides, most people use a water based acrylic. When you paint the inside, you have to paint the layers in reverse of what you would do on the outside. Meaning that you would do the details first, then the base coat over that.

Automotive paint is just what it says, but it’s not the touch-up stuff you get at Pep Boys etc. It’s professional grade like used in body shops.