I remember when this chart first appeared. The thing is, a microphone that's "transparent" (at least as I would use the word, meaning that it doesn't audibly change the sound that it picks up) by definition can't be either "bright" or "dark." Or another definition could be that "color" = upper midrange response while bright vs. dark = high-frequency response. But either way the logical problem is the same. The field ought to be triangular or wedge-shaped, starting from a point of convergence on the "transparent" side and growing taller toward the "color" side.
And unfortunately, either way, many of ratings seem to be just plain cuckoo wrong. Plus, in many cases the person just put a manufacturer's name on the chart as if that company only made one microphone type that mattered (e.g. Schoeps and DPA). In other cases he put a model number with the name, but that model has multiple capsules or pattern settings that sound different (e.g. the AKG mikes).
The sad thing is, this chart has axes that are at least potentially definable objectively, and if someone were to state those definitions clearly and measure the microphones under fair and equal test conditions, a scatter chart might really tell the world something useful. And that wouldn't even be super-hard to do, at least for the on-axis response of the mikes.
Of course, then I'd want to see a similar chart for diffuse-field response, since I don't do much of my recording work in anechoic chambers--for some reason people just don't put on operas and recitals in them ...
--best regards