thanks for the question! Story time!
4 pictures under spoiler button.
First is now around 12 years old, the miniatures and paint being even older. (puuh, time flies by!)
Picture shows my original colour scheme back then, it was heavy inspired by a ultra highlighted Whitedwarf army paint back in the day. (But I have seen the japanese paint scheme you talk about, but the actual WW2 inspiration is from the Battle of Berlin era Panther Is and IIs)
Additional reason would have been, that I did not have "red themed" army back in the day. As I had yellow Imperial Fists, Blue Eldar, Blue/White Sisters. Idea was emphasized by a Mars iron oxide based terrain camouflage.
2nd pic shows my Converted Callidus assassin, which I employed im my match. Furthermore, picture presents, repainted commanders from first pic.
3rd pic actually shows my modern Imperial guard... I mean Astra Militarum Camouflage. The red is actually a bit distorted. It is old Redgore base and Bloodred highlights. Left Platoon Commander, middle: Company Commander, right: regular trooper.
Due to their fluff they have Fleur de lis on their shoulders. (I won't get into that any further.)
4th and last picture presents, my old paint scheme on the Canoness (good old days while they had jump packs ) . My current Imaginifer banner on middle and finally on the right the "modern" paint job of the sisters of battle. Canoness will eventually get her touch up, up to date, after I finish all the unpainted ones... Which I still have a substantial amount...
Speaking comes by nature, silence by understanding.