This question, in addition to a player of mine who recently wanted to play a Lawful Neutral Fallen Aasimar (but ended up doing something different), got me thinking about something…

Playable Aasimar (from Volo's Guide to Monsters, pp. 104-105) have three subraces; Protector, Scourge and Fallen. There is some flavour text that describes that Fallen Aasimar tend to be evil, but it's not clear whether they must be evil, and conversely, that the other two must be good, and that a Fallen Aasimar cannot be good, etc; and where does a neutral Aasimar fit into this?

Something that jumps out at me is the flavour text for Fallen Aasimar (all emphasis mine):

An aasimar who was touched by dark powers as a youth or who turns to evil in early adulthood can become one of the fallen–a group of aasimar whose inner light has been replaced by shadow.

— Fallen Aasimar; Volo's Guide to Monsters, p. 105

The "or" implies that being evil isn't the only way to be a Fallen Aasimar, so in theory this means an Aasimar who happened to be touched by dark powers but fights against their influences on them could be an example of a good Fallen Aasimar. So is that evidence enough that Fallen Aasimar can be good after all?

Another thing that jumps out at me is this side bar (all emphasis mine):

With your DM's consent, you can change your character's subrace to fallen aasimar if your protector/scourge aasimar turns to evil. To do so, replace your subrace benefits, including the ability score increase, with those of a fallen aasimar.

Similarly, if your fallen aasimar turns to good, your DM might allow you to become a protector or scourge aasimar.

— Falling from Grace or Rising to It; Volo's Guide to Monsters, p. 105

This seems to imply that the intent of a Fallen Aasimar is actually that they are inherently evil, or at the very least, inherently not good, so much so that being good "forces" (I say "forces" in quotes because this is explicitly called out as needing DM approval, but I'm trying to interpret the flavour implied by this information, rather that care about the people in real life around a table) them to no longer be a Fallen Aasimar. So then, Fallen Aasimar can't be good, and "should" be evil.

So, from what we know about Aasimar:

• Must Fallen Aasimar be evil? Or can they be neutral? Or even good?
• Must the other two subraces be good? Or can they be neutral? Or even evil?

Again, I am after what the intent is based on what the rules say, ideally backed up by any other official information on aasimar out there; I'm not interested in whether a DM can allow these things, since the answer is always yes, but rather what the intention is inferred from what information we have (since I don't want this to become a designer-reasons question either).

In other words, this is a "how do you read these rules" question, not asking for opinions (designer or otherwise) or asking for something that can be answered by "ask your DM/you're the DM, do what you want".

(As you can see, I'm trying to avoid something that will get closed as off-topic or similar; any suggestions on how to make this a better fit for RPG.SE are welcome, if my efforts thus far aren't enough, since it really is just drawing conclusions from the rules that I'm after here…)