I've found that PVC can be best colored with clothes dye. Although spray painting will work, it isn't nearly as durable.
I suggest RIT brand clothes dye... simply heat you PVC up in hot water, allowing the temperature to balance throughout the pipe.
Add the clothes dye, (powdered form), and stir to distribute the color. The longer you leave PVC submerged and exposed to the dye treated hot water, the darker the resulting color will be.
You can buff it afterwards with a non abrasive car wax to produce a water repellant shine. Very nice indeed.
If you must paint, Krylon makes a spray that claims to bond to plastics. I tried it on some scuffed MC fenders a while back and was'nt too impressed with the longevity. The pressure washer didn't forgive it either.
Try the clothes dye method... when done right, the results will impress you.
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Shorts... little pants, only shorter.