If I was buying new seats they would have to be red. But at the end of the day - It doesn't really matter, just go with what you like more. I would quite happily put black seats in my car if I got them second hand and on the cheap.
I would lean more towards black as it's not so 'in your face'.
If you still have the red door cards/carpet in your 9 then you can't go wrong with red really.
But as said, it's your decision.