Well, best practice is to roughen the surface through media blasting. I have a couple of frames that are obviously fully chromed, and you can see the areas that were painted had been media blasted after chrome. Here's a perfect surface (not chromed), ready for paint:

https://cimg7.ibsrv.net/gimg/bikefor...b5f37fc8c2.jpg
Photo courtesy of Brian Chapman's flickr site.

Years ago we had some custom office cabinets made in Celeste, using Imron. Being a design shop we tried to match it with the Pantone system and it took a few passes to get it right. We eventually brought a Bianchi bike to the paint guy for matching purposes. It's often difficult with Pantone, since they use special colors like "Reflex Blue" that are difficult to match correctly using 4-color process. As many have pointed out, Bianchi wasn't exactly consistent with Celeste, so it's good to have a sample of your favorite Celeste. We used a particular bike.

Sit around with a bunch of framebuilders, you'll get the same story about color.

I've done a several 650b conversions for different people, the conversation on what braze-ons to add, trail to add to the fork, fenders, wiring, etc usually takes an hour.

The decision on color takes 4 weeks.

Several framebuilders I know have a list of colors that they'll powder coat/paint to for a set price, choose something different and the price increases significantly. There's really no cost savings in the paint to standardize on the very small runs even the most prolific framebuilders do. The amount of time talking to the client about the color is why they charge more.