It's to do with positive and negative space. When you look at an object and try to make out the outline of the shape, you're looking for positive space. The wing stands out and that vortex generator at the roof line stands out. The overall shape doesn't get "lost". Grills and vents being black is fine, because they emulate openings. If anything, those are negative spaces that help bring out the overall features of a car.
https://cdn.carbuzz.com/gallery-imag...uzz-410953.jpg

Many hot hatches are doing the black wing thing, and Veloster N is one of the worst culprits that go beyond just the wing. You look at this and it looks like the rear bumper is missing when your eyes try pick up the outline. I like to do something I call the "squint test", where I squint until my vision gets blurry. Most of the blacked out areas will lose it's "detail" and what you're left is really the outline of a car. Often when a car is cruising by, the outline is really what your eyes is going to pick up. I think this effect can also work when you just simply reduce an image to a thumbnail size. Cars like the FK8 won't really be affected because the areas that should be positive spaces aren't blacked out.
https://cdn-ds.com/blogs-media/sites...ide-View_o.jpg

and lol, Elantra N. It's not so much that the bumper is actually that ugly... it's the fact they made the entire thing "black" so it looks like a huge hole. The Elantra N in the background is out of focus so it's a bit blurry, but holy, the front bumper doesn't look like it just has an opening in it. It looks like the entire thing is an opening.
https://www.autoguide.com/blog/wp-co...t-Featured.jpg

For comparison, the mid tier Elantra N Line has a very similar bumper, but it's not all blacked out and it looks a lot better. The bumper really is basically 95% the same design, with only the difference of where they "strategically" black out or leave body matched coloured. Simply the power of colour, can make such a drastic change.
https://static.carindigo.com/images/...0f3aecf374.jpg

Because black things look like holes or void spaces, black should be more cautiously used from a design aspect imo... otherwise it just gives the illusion things are missing or there's holes in areas that shouldn't be.

It's basically why the new WRX looks so nasty. The whole blacked out cladding area makes the wheel well look a lot bigger than they really are, and at a weird polygonal shape like someone ghetto hacksawed the wheel arches. The whole car looks lifted because there's just way too much black surrounding the tires. Try the "squint test" on this one.
https://cdn.motor1.com/images/mgl/l9...subaru-wrx.jpg

Body painted wheel arch WRX to the rescue:
https://i.imgur.com/4HKdEtS.jpg