Angels Cerulean fluff critique

[Phiasco]

Hello all. So I'd like to make a successor chapter who's color scheme is similar to the forgeworld alpha legion paint scheme. It's my favorite paint scheme I scene so far. However, as I'm just as in to 30k as 40k I'm trying to come up with some passable fluff justification for their armor to be colored this way instead of standard legion red. So please pick apart my fluff explanation and suggest more credible/cinematic story elements.

 

So, this particular chapter of the IX legion astartes wears different colors then the rest of their brethren. This tradition dates back to when the entire chapter was deployed to a hive world to counter a large xenos incursion. Intelligence was wrong about the threat level posed by these xenos. The defense of the planet quickly became a route. The chapter was split into numerous holding actions, buying time for government officials and the civilian populace to evacuate the planet. In the end, the few survivors of the chapter who made it off planet looked as if they had bathed in the filthy xenos blood. As their armor was taken care of by the chapter serfs, it was discovered that the xenos blood had had a peculiar reaction to its ceremite plates. It had chemically stained the armor a light blue. Upon hearing of the noble sacrifice made by those of the chapter to allow others to escape from harm, Sanguinius made a decision. From that time forward, the chapter would wear that same color, to honor and remember that sacrifice. The oldest veterans don't have to have their armor painted, as they still wear that same chemically colored armor. Eventually, those suites of armor would become sacred relics of the chapter. 

 

....or something like that. Like I said, pick it apart, throw me some suggestions. When someone asks why my 30k blood angels are blue I want to have a good story ready for them. 

[Tyriks]

I'm not at all involved with HH stuff so I might be way off base here, but I think it would have to be something bigger than saving some people for Sanguinius himself to say part of his legion has permission to have completely contrasting looks.

 

What if whatever action it was that stained the armor happened in such a way that they were cut off from the rest of the Legion and now they're fighting to reconnect with them? In 30k games they simply haven't had the chance to repaint their armor, and they either never catch up or don't until the siege of terra, and by the time they would fix it they are officially a second founding chapter and choose not to.

[CaptainHelion]

If you're planning on playing in 40k only, then there's no need to have any special dispensation for the colour scheme. You could have them take their scheme from the story you've come up with, but say that they're taking inspiration from those warriors, rather than being them?

[Phiasco]

Captainhelion, I am planning to be in 30k just as much as I am in 40k, hence the desire for some good backstory fluff explanation.

 

Tyriks, it's not just that they saved a bunch of people. It's that out of an entire chapter, only 15-20ish marines survived. It's more about the tremendous sacrifice made.

[CaptainHelion]

Fair enough! Are you planning on using them as both Legion Astartes Blood Angels and Codex Blood Angels, or as LA in both systems?

[Phiasco]

30k rules for heresy games, 40k for 40k games.