The premade lenses are painted by machine and simpler than the more expensive lenses. I've never used this company, but they claim to follow FDA regulations. When you try to order, the site should ask you for a size and to send them a doctor's prescription (even for noncorrective lenses).
When a color is over the pupil, your vision will be tinted, but you'll be able to see so long as the color isn't opaque, much like wearing rose-colored glasses and such. Don't drive with them