The first example is “go ahead, try to find the single C0 in these bytes” and then argues one should highlight C0 bytes.
If that’s true, how does the tool know I will be looking for C0 bytes and not for 03, D3, etc? The logical conclusion of that would be that the hex editor should uniquely color code every byte. And following the other examples even that’s not enough.
The proposed solution is to create groups of byte values that each get their unique color. I think that helps, but we can do better: add a search feature. That tells your editor what you are looking for. Once you enter a search string, it can highlight all hits.
Yes, “colorful output in a hexdump is useful for the same reason that syntax highlighting for code is useful”, but do you know what syntax highlighting needs? Knowledge of the expected content of a file. Without that, a hex editor at best can guess at how to color-code stuff.
IMO, if you want to add syntax coloring to a hex editor, give it pluggable syntax coloring and heuristics for deciding which one to use when.
While at it, also let those plugins control where to break lines, whether to show hex at all (why show it at all if a file has a few paragraphs of English text or an array of IEEE doubles?), etc.
Those plug-ins will make errors and sometimes, users will want to see all byte values, so you’ll need a way for the user to override them.