I’d also like to point out that this isn’t just an issue with custom URL scheme type things (the addressbook:// format). I’ve run into issues with it when trying to make an internal link to a header that includes a colon, with Markdown links on (Wiki links off). For example, try to link to a header:
# Test: This should fail
(In my example, I used the [[ syntax to start making a link, then typed # to get the headers in the current file, and selected the appropriate one.)
it generates a link that Obsidian interprets as an external link. The resulting Markdown is
[Test: This should fail](#Test:%20This%20should%20fail)
If I replace the colon with either %3a or %3A Obsidian recognizes it as an internal link, but can’t follow it. When I try to hover-preview the link, I see the error
Unable to find the section #Test%3a This should fail in <file>
So it looks like Obsidian’s internal link system doesn’t understand this encoding, or something like that. So I’m not sure how you’re getting the colon to work in your examples? Unless it is something messing up the internal link system.
I will also note that if I use angle-bracket links, the colon doesn’t get recognized either. The syntax
[Test: This should fail](<#Test: This should fail>)
is still interpreted as an external link. If I remove the colon it works fine.