I have no information about Color so I'm not saying that necessarily happened, just that it's a way of reconciling all the conflicting stories. The submitted story on its own doesn't quite add up either ($2M for 20 employees is too low).
Maybe I just don't understand how these things work.
They're hiring a team of software engineers who have been working together for a while in an area which is clearly of interest to Apple (I'm betting they're going to be working on Facetime).
They've been working with live video extensively. They know the lay of the land. It's very valuable.
And if you want to acquire this many engineers from a company simultaneously you're probably fighting against a huge amount of non-competes, so approaching the company and negotiating directly for the hires is the best way to avoid getting slapped with a lawsuit.
 What is interesting, though, is that they may have legal reasons for this. Any extant creditors, for example. We may see a second stage disposition of the IP. Transfer of people for $$ != transfer of legal-owned Gaap assets, when it comes to fraudulent transfer. Relevant > http://en.wikipedia.org/wiki/Fraudulent_conveyance
Maybe the employees signed a non-compete agreement, and what Apple is buying from Color is a waiver on those agreements? Non-competes don't have a great record of standing up in court, but OTOH $2 million split 20 ways isn't that much money per person either; might be considered cheaper than the risk of a legal challenge. I dunno.
The reporting on this story could definitely do with some additional detail, but given how rapidly the story's been changing we may just have to wait an hour or two for that detail to be uncovered :D
The employees, of course, are free to walk away from those unvested options and retention bonus, should they chose to do so.
Engineering talent isn't always correlated with great organizational awareness, so while some of the better people will have moved on by the time it gets to this stage, there will still be strong engineers left.
That being said by this stage it is unlikely to be a team on top of its game, and if the stories about an increasingly poisonous work environment are to be believed, Apple is going to have to do a winnowing process, and keeping the "team" together may well be counter productive.
 Informal acquihire in the sense that our CEO got wind of a company closing down its remote sub (remote to them, local to us) and made a blanket offer to the team
The tales of double-digit million dollar exit were frankly baffling and would have painted a very different picture of the current acquisition market.