One thing to not about all color matching is translucence... which has something to do with primer, so I could see why someone would mention it in the context of color matching. Paints, dyes, pigments, stains, all have different bases, with different levels of opacity. Some acrylic colors have a white base, which is usually totally opaque (non see-thru.) Colors like ultramarine blue are much more translucent, so it's very difficult to get a bright smooth coat of it, without really, really knowing what you are doing. Many of the cool / vivid colors are this way. Any color with a little translucency is going to be very tough to use over the top of something else without having a bleed through. A coating of white primer (or white canvas, etc) will at least get your translucent color a good place to start.
Anyway, that being said, it's tough to get an index of translucency of your average home store paint. Fine art paints sometimes make mention of it. It's odd, though, I would consider the pac color one that could be based off of a white and totally opaque base... thus making it easy to paint over the top of something else, and immenently matchable.
There's a lot of other stuff I'm not mentioning about color matching, color theory, or real world application of paints here.
In general, I am surprised that you can't get a reasonably matched paint of that particular color. I guess, though, many times color matching is very difficult... it takes a human to really get it right, and a human that really knows what they are doing, might still be off a bit.