I have vynl siding that I want to paint. Do I have to use a special paint or primer to do this?

Some major paint companies are making coatings for painting vinyl siding. Sherwin-Williams makes a latex called WeatherPerfect that is supposed to bond well to vinyl. I would definitely use one of those rather than plain latex. There are some cleaning requirements that need to be followed to insure a good bond.

Yes and you will need to properly prep the vinyl siding before you paint. And there is special primers and paints for this. Check with a Paint store not the big-box ones as they have the products you need.
You will need to powerwash the siding and get the haze off of it as well as any soil that has stuck to it over the years.
Then there is a pre-prep solution to the process that etches the vinyl so the new paint will bite into the older vinyl material. Once that is done then a special primer is applied, Then the final color. This all needs to be done in a very short time period, otherwise you will need to re-prep again before you put the final coat of paint on. This is really a job for a painting contractor with a fair amount of help, not a homeowner with only one or two people doing the job.
One suggestion however. Do not change the color of the siding. Keep it the same as it is. Two reasons for this.
1. Making a change of color will be difficult as the overlaps of the siding are not the same color. As the vinyl expands and contracts the unpainted areas will show up where the siding overlaps itself.
2. Making the siding a darker color will cause more expansion during the sunny days thus causing more movement and the joints will show more where the paint was not applied.

Personally I would not do it. Unless your planning to sell and you want the curb appeal. Regardless of the manufactures claim, the paint will peel off, fade, and chaulk. A proper paint job may end up costing almost as much as a new siding job anyway. Simply power-washing the siding may bring back the look your trying to gain by painting.