When I grew up, "loud" was not so much about color (unless it was neon) but about clashing (which sounds loud): orange shirt and red pants, madras pants and flowered shirt.
Aziza: fascinating.
Moses: interesting idea about the warning colors.
Decades ago, the prostitutes in Russia used to wear red stockings to advertise.
In the far west of Ireland, where life was stern and earnest and clothing ferociously functional in general, a traditional attire for a woman as late as the 1950s might well be black hood, black shawl, homespun shift (functioning as blouse and slip), black skirts, and bright red petticoat.
The use of red in military uniforms was said to disguise the blood after injury.