(Should we do PHUIColor at some point?)

This looks like it colors by event creator PHID, but this seems like it won't be too meaningful after events can have multiple invitees. Fine for now, but we might just want to color each event instead or something?

I think this is unused.

You could either make $allblue work and skip this part, or do something like:

$eventcolor[$phid] = $calcolors[$i % count($calcolors)]

...so that the color loops around to the beginning again and we get a nice rainbow.

It's slightly more correct to pht() this now:

pht('%s (%s)', $name_text, $status_text)

If either $name_text or $status_text contain markup in the future, the pht() version will work while the non-pht() version will convert the markup to strings and escape it. This will be safe, but produce the wrong result (overescaped text shown to the user).

This could be simplified to just $status_text without the string.

We can remove this transaction stuff now too, this block can just read (after the EpochException check):

return parent::save();

(Maybe this should happen one level up? There's no way for something rendering this to say "I'm going to render <em>No description.</em> if there's no description, since I'm always rendering the name above it" since it won't be able to tell if the description is missing.)

A strlen() test is slightly more correct, in that it will behave like users expect for the description "0".

You should include:

if (!$user) {
  return Aphront404Response();
}

...after executeOne().

Maybe this should be withInvitedPHIDs()? They mean the same thing right now, but in the future they won't.

Likewise for this, withInvitedPHIDs()?

I'd expect this to sort on start, not end?

This isn't quite correct on leap days, etc., but we can clean it up later.