red uniforms

Well, it's one of the colors in the British flag, but red is in almost every flag, so that probably doesn't mean anything.

My guess is that it was intended to conceal blood. Doctors (or is it just the patients) today wear those ugly green smocks. The reason for that color is that it's the exact compliment of the color of blood. When the two mix they visually neutralize, making the blood less obvious, I guess. At least that's what they told us in a lecture on color for architecture.