There is an important distinction to make which may (but also may not) be relevant here: the various flora have different geological requirements, and can have preferences as well. Like an example, a species might appear on silty and sandy rock, but be more frequent on the latter - and not appear at all on gravel. Or another species might want quartzite specifically, while for a different one it's just metamorphic rock, and so on.
Personally, I suspect that the shades might be tied to one of these preferences... but then there's the quoted dev post. Although that could be wrong too - it wouldn't be the first time in history that a company employee made a mistake on reporting about some aspect of their game.
In either case, what does work is that where the map isn't coloured, that's where you shouldn't look. That's it. Anecdotes aren't evidence, and I'm not aware of anyone gathering data on the DSS map. It'd be a large and time-consuming effort anyway, and for not much reward, because the problem of not finding a species somewhere can still be solved by flying to entirely different-looking areas.
It's rather like the problem of Clypeus Lacrimam and Speculumi. I won't go into detail on that here, but suffice to say, which of the two is present can't be determined from the journal info alone. (After all, the game doesn't write the maps of a planet to disk.) You can estimate very well from the DSS map which of the two it'll be, but to be certain, you still have to fly down and check. Now, with plenty of data collection, we could work out the geological requirements, and then go from "the Clypeus down there is either Lacrimam or Speculumi" to "the chance for the Clypeus down there to be Speculumi is 78%, or Lacrimam at 22%", but to be 100% certain would still require landing. So, researching that would be an enormous amount of work, and for little reward, because there's not much time to be saved. Flying down from orbit to the surface doesn't take long.
Moving back to what I said earlier: my advice tends to be two things. One, don't look in the non-coloured map areas, that's what's for certain. Two, if you don't find what you're looking for after a couple of minutes, go farther and check different-looking places instead. It doesn't take long to fly a decent distance, after all. (You aren't flying an Anaconda at 250 m/s, right?)
And hey, with advice two, at the very least you'll have some more variety for screenshots!
