What do they mean? Nobody knows, all I've ever read is spray pattern, don't mix them, basically a bunch of speculation. I've replaced quite a few VG injectors, but only on fixer uppers from craigslist. Never paid too much attention to the dot colors because frankly, the cars were going to be sold anyway. I don't even remember if replacements I installed matched or not on previous cars, it's been a long time since I've flipped one.

Not until now have I been forced to replace injectors on my car. I tore into it yesterday wondering what the dot colors were. And guess what? There were 5 blue dots and 1 black dot. Big deal right? YES, because I bought my car with 87k miles on it and there were absolutely NO signs of the intake ever being torn apart. All injector screws looked the exact same, everything equally weathered and dirty, literally nothing had any marks or nicks that would indicate injector replacement. So what I'm saying is, the car came with 5 blue dots and 1 black dot from the factory. Considering there is no way to find out the dot color a car has, even with the VIN, on top of these findings, I've pretty much come to the conclusion that it really doesn't matter, regardless of the urban myths about spray patterns. As long as you're not mixing flow rates (VG/VE). It's possible a highly skilled mechanic who leaves no trace of his work once replaced a single injector on my car before I bought it, but I doubt that's the case. The injector screws are the main thing, they are virtually impossible to remove without nicking or semi stripping the head. In fact, vice grips are a must to break them loose. Regardless, it's ran fine for god knows how many years with a black dot mixed in with 5 blue ones.

For the record, no. 3 and 4 went out completely within a month of each other. I went in thinking I would only be replacing those two, turns out only 2 of the 6 were within spec. Luckily I had exactly 4 used square tops that were within spec so I replaced them all. I was planning on swapping to the set of ovals that I picked up a month ago, but I figured I'd use these up before buying new insulators, swapping connectors and getting ahold of the lower collector plate. I just wanted to get it running on all 6 again as quick as possible. So far, it's running smooth as ever, now with 3 blue dots and 3 black dots.