They had a documentary on Foxtel several weeks back about colours - fascinating stuff.
It claimed that red is the number 1 colour that appeals to humans full-stop and this goes back to the early humans. It symbolises blood etc. and it apparently creates like a primeval response in humans.
That was the reason given for it's popularity around the world as sporting clubs colours.
Yes, and I can speak from experience. I chose Essendon as my club when I was 5 BECAUSE of the red. At the time, I wouldn't have known why, but research shows that it's an appealing, powerful colour. Almost a scary colour that you would subconsciously want on your side, hence why people choose it. Primeival might be a good way to put it, as as you say.
The three most successful EPL clubs historically (ManU, Liverpool, Arsenal) all wear red.