Upon taking a closer look at pictures on
FFG's website (who invented this Chapter), you are probably right. It looked rather white from afar, but I can definitively make out a metallic reflection
here.
Still, skies during a storm are grey rather than blue.
The Fleshtearers have a rather cool and tragic background, by the way. They're essentially a condemned Chapter, just a step away from being excommunicated and purged, and with half the Marines being berserkers who are at risk from turning into frothing cannibals at a moment's notice. Chapter Master Seth seems to be one of the few sane guys left, and he spends day and night thinking of a way to save his boys from their impending doom.
Here is some background on them from an old Index Astartes article in
WD #251.
Also, totally not related to a
DW character of mine, but I heard from a reliable source that the
Celestial Lions have a very cool and unique colour scheme!