I have always had a curiosity with red and black. I have always thought it was a little weird as well because that combination doesn't always display "friendliness".

I think I know why though. For some genius psychologist this may be elementary but I think it's due to animal instinct and a perception of ourselves really.

black equals darkness, which is the fear of the unknown or that which we cannot see. animals like us stay hidden at night because it's fear that drives them to keep safe.

red equals blood, which is the obvious sign that our bodies have suffered trauma. we know what will hurt us so we stay away from those things. again, it's the fear that keep us safe.

this is why red and black have the most power.