The tombstones at the end of the desktop and mobile articles look like characters that the browser can't render as opposed to the Nat Geo tombstone. (See attached screenshot.) This is a good example of something that doesn't translate very well directly from print.
Please change to yellow. You can get the official Nat Geo yellow from their logo.
It doesn't look like the image captions are using hyphenations. Hyphenations will increase the "resolution" of the exclusion and make them look sharper.