For the record, this is how I run any heavily obscured area that is adjacent to a less obscured area. Describing transparent blobs really doesn't come into it, nor do I think it's necessary for this approach.
This is only partially true because opaque objects like vegetation do block line of sight to things behind it. That's because 5e oversimplifies everything and some genius at WotC thought it wouldn't be a problem to have natural darkness, vegetation and fog working under the exact same mechanics.
Yeah, that cannot possibly be true. But let's keep in mind that according to the Player's Handbook, if you replaced the trees with a patch of natural darkness, Dog would still be unable to see Bunny.
This is only partially true because opaque objects like vegetation do block line of sight to things behind it. That's because 5e oversimplifies everything and some genius at WotC thought it wouldn't be a problem to have natural darkness, vegetation and fog working under the exact same mechanics.
I'm not sure I understand you. If dense vegetation is blocking line of sight to something, then that thing is either (a) in a heavily obscured area or (b) not part of the play area and so not described or relevant to the situation.
I'm not sure I understand you. If dense vegetation is blocking line of sight to something, then that thing is either (a) in a heavily obscured area or (b) not part of the play area and so not described or relevant to the situation.
But please notice that natural darkness is also transparent and the game still treats it as heavily Obscured even when creatures inside it are casting silhouettes all the same. Not sure why you couldn't just describe the visuals as you would any normal unlit area. Besides, the transparent darkness has precedent in previous editions and the weirdness of the visual effects were never an issue before.
The vision and obscurement rules are very abstract, treating light levels as a constant at any particular location rather than taking into account the relative positions of observers and light sources. There's two broad ways (with infinitely many variations and intermediate approaches) a DM can approach this:
DMs can treat the rules as an abstraction, sticking with them when they make sense and deviating from them when they don't. In such a case, a backlit creature in a naturally dark square would be visible by its silhouette and thus, by definition, not heavily obscured.
DMs can treat the rules as defining the physics of how light works in a D&D setting, and go with them regardless of whether or not they produce outcomes that match real-world understandings of what would or would not be visible in certain circumstances. In such a case, a backlit creature in a naturally dark square would be heavily obscured, by definition, and thus observers would be "effectively blind" when trying to see that creature, rendering the silhouette unseen. Under this approach creatures would never be visible as silhouettes, since any creature would have to be standing in at least dim light for the silhouette to be visible, but in dim light the creature would be visible as more than a silhouette anyway.
Either approach has (surmountable!) problems when trying to describe the visuals of the Darkness spell "as you would any normal unlit area".
In the first approach, backlit creatures in the area of the spell are visible as silhouettes, which contradicts the rule that creatures in a heavily obscured area are not visible (because observers are "effectively blind" when trying to observe them). (This issue doesn't arise with natural darkness because under approach 1 the DM simply rules that creatures visible in natural darkness as silhouettes aren't heavily obscured in the first place.) This issue can be surmounted by nerfing the spell and ruling that backlit creatures in the area aren't heavily obscured after all.
In the second approach, backlit creatures in the area of the spell are not visible. The spell effectively thus creates a sphere in which observers are "effectively blind" with regards to everything in the area, but not the areas behind the darkness, making everything in the area effectively transparent. This directly conflicts with the description of the spell that describes it as creating darkness that fills a sphere and says nothing about making creatures or objects transparent. Additionally, if the spell has the effect of rendering creatures and objects transparent, there is the additional problem of what to do with barriers in the area like walls and floors. Observers are "effectively blind" with respect to them too, but not to the areas behind them, so in theory they should also be rendered transparent, but that produces the absurd result of letting the Darkness spell allow observers to see past opaque barriers into lit areas beyond. (This issue doesn't arise with natural darkness, because there is no spell involved that needs to be interpreted to have a consistent effect that matches the spell text.*) This issue can be surmounted by being ok with the radical departure from the descriptive text of the spell. The walls/floors issue can be surmounted by ruling that the transparency produced by the spell is directional, and only applies when seen from directions in which there is a backlight, and that creatures/objects/walls/floors remain opaque when viewed from non-backlit angles.
A super-literal version of the second approach could, if taken far enough, produce the "effectively-blind-with-respect-to-an-unilluminated-wall" x-ray vision problem with natural darkness, but I'm assuming no DMs go that far.
If instead the darkness created by the spell is opaque, neither approach to the vision and obscurement rules produces a problem.
I would also note that any interpretation that treats the darkness created by spell as transparent has the problem that the darkness itself can't be seen, which arguably conflicts with the description of the spell as creating darkness that fills a sphere. This is surmountable either by being ok with the created darkness being unapparent to observers, or by, e.g., making the darkness only partially transparent so that its scope is still visible.
As for why the 3.5 version didn't have the same issues, that's because the spell fairly clearly described a situation where affected creatures and objects were visible as silhouettes, and provided explicit game rule effects for how to treat those silhouettes (i.e. 20% miss chance from concealment). 3.5 also lacked the "effectively blind" language in its vision rules that produces so many complications in 5e.