The colour black

[Nathan Ross]

I heard a story about a general waring black with this being considered a bad omen by his soldiers and him loosing the battle

That was Crassus before the battle of Carrhae (Plutarch, Life of Crassus, 23.1)

The story (whether real or not) illustrates the problem with black - it was indeed associated with death, but not in the way we tend to think of it today. The Roman association was with loss, mourning, and very bad omens. They did not think of it in a 'goth' sort of way, as something powerful or terrifying.

So there would be little reason for soldiers to wear black to strike their enemies with fear and awe. Roman military culture instead accentuated bright colours, flashy polished armour and bling-covered equipment; that was what they considered impressive and terrifying, not deathly black.

(Then again, there is a picture from the early 4th century Roman principia at Luxor showing what appears to be a senior officer dressed in a short sleeved black tunic beneath a yellow-brown cloak, so perhaps it wasn't entirely unusual. Unless the man concerned was on his way to a funeral, perhaps?)