But ... if I don't see the color on the car, I can't tell a darn thing.
Beautiful color on the Infinity ... but until I look at it on your El Camino, I can't see in my minds eye what it will look like. I'm just not wired that way.
On the flip side, if you can pick out a color from that website all you have to do is walk into any bodyshop and tell them the year and model and boom, you have your color. No flipping through books trying to find something close.
I picked my color out of a book, but until I saw it painted on something ... those fuel rail covers ... I wasn't sure I was going to like it. I thought I would, but I couldn't see that gray over black until I could see it.