Changing a speaker color

If the original paint is in good condition, it does not need to be stripped, only sanded to a matte finish. After removing all sanding dust, the original paint should function perfectly fine as a primer, assuming it had an automotive-grade finish to begin with. 

Remove the drivers and binding post plates prior to any of this of course, and mask off the holes. 

There is no way to achieve a true piano grade finish without a very controlled HVLP spray system/gun. I recommend that be handled by a professional, otherwise you’re likely to end up with runs, orange peel effect, or trapped debris.  
 

@akg_ca you underestimate the talent of many home enthusiasts.  While I am not a painter, there are many areas where I do the work myself because my work is better than the pros.  

I don't know about @jeff7630 but I wouldn't assume he is talentless.

Second, used speakers sell at half of new anyway.  if the paint isn't perfect, you still can get 7/16 of new. Don't pay 40% of new for a pro paint job.

And changing from an unusual color to black, probably improves resale.

Jerry

What’s 7/16, a new grading system ? 

Depending on what color you like, I've sometimes considered using a vinyl wrap instead.  Removable. 

I would also recommend doing the vinyl wrap. Similar to what they do with vehicles.

It is very durable, has no problem being applied to a high gloss surface and can be removed if circumstances change.

Added bonus is that you can literally any surface treatment you can imagine. All you need is a digital file.