As those two points seem quite divergent, allow me to ease into the matter more slowly. First, from Sazed's comments in the HoA bumps, we know that black is the color of Ruin, and white is the color of Preservation. Thus, we have two colors already established for us.
Second, there are (at least) two other important colors that have been identified in the books: Red and Gold. Namely, these form part of Miles' prophecy at the end of Alloy of Law. If we knew what shards Red and Gold represented, we would have a hint at what is coming to Scadrial.
Third, based on this, we know that Ruin and Preservation have a past relationship with "Red." The chapter 9 (Damnation) bump from tWoK's is as follows:
Ten People, with Shardblades alight, standing before a wall of black and white and red.
I am proposing that black and white here are referencing Ruin and Preservation (and likely Ati and Leras specifically). This gives us two other shardic actors, though. Red and the 10 people (the heralds, presumably, in place of Honor).
The three colors in the wall seem to be particularly important in the light of another quote, this time from the 11th chapter of tWoK's:
Three of sixteen ruled, but now the Broken One reigns.
Unfortunately, the first part of this quote can be taken 3 different ways. Shards each seem to have a number associated with then. Honor, for example, is 10, while preservation is 16. So, "three of sixteen" could mean 3 individual members of the group of 16 shards, or it could mean Shard#3. Because the Three seem to be an important part of Rosharian mythology, I am inclined to assume that it is referring to three different individuals. As such, these three individuals seem likely to be the Black, White, and Red mentioned before.
Support for this comes in two different forms. First, The Letter states that Ati was once a good person, which one would hopefully want in a leader. This is a very brief description, admittedly, but we can better believe that Ati once ruled than, say, Rhyse.
The second support is in the first quote. Ten people are standing before a wall. Given the numerical significance, we can be fairly sure that these are the representation of Honor. Is honor standing in opposition to or in defense of the wall? Given the emphasis on knightly defense in tWoK's, it seems more likely that Honor is here on the defense, protecting the wall.
Further, if we take Black, White, and Red to be the 3 of 16 mentioned who once ruled, then it is likely that Honor would be honor-bound to them. Indeed, it is unlikely that Honor would have subverted them (though possible). Yet, we are told that "The Broken One" now rules. This could reference any of the shattered shards, but again, given that this is in tWoK's, it seems likely that it is referring to Honor.
So, then, it seems likely that Black and White (that is, Preservation/Leras and Ruin/Ati) once ruled (along with Red), with Honor as a sort of royal guard.
Who, then, is Red?
That answer, I believe, is in Elantris. The Derethi, whom are generally believed to be followers of a religion influenced by the existence of Skai/Dominion, wear a lot of red, and red seems to generally be a holy color for them. Thus, Skai/Domination appears to be the most likely contender for who Red represents.
If we plug this information in to the various quotes, that would mean that Domination, Ruin, and Preservation were a triumvirate that ruled at one point, with Honor as a sort of guard. If that is correct, perhaps then Odium has a grudge against the Triumvirate specifically? Honor would have been shattered first, as he was protecting the others, then he happened to attack Domination first, and will now turn his sights to Ruin and Preservation. That doesn't explain why he left Cultivation intact (if she is intact) while shattering Devotion, however.
Additionally, Miles' prophecy then means that we should expect to see Skai/Domination agents on Scadrial, eventually, along with "Gold"'s agents.
Who is gold?
There is currently no good answer, to my knowledge. It may be Honor (as that would fit with the people before the wall imagery), but I haven't seen anything in tWoK's that strongly suggests that Honor is linked to gold, and I haven't read Warbreaker yet. That would make sense, however: the remains of a former protector would have reason to continue to defend the remains of a former lord, yes?
The other shard that we have a hint of color at, that I am aware of, is Aona. Both blue and silver seem to be fairly common in Elantris, but, unfortunately, they don't seem to be as commonly present as Red, so that might just be random chance.
By any chance does anyone else know of a color related to a shard or hints about the cosmere that might be referencing shardic colors?