I think the (flat) black spoiler on a red car would look badass, just like way back in the day of the '69 Mach 1.... my friend has a red one and it looks perfect for the car and I think you'll get the same results with yours.
I have a black spoiler as well and love it!!! It matches the rest of the car...
the more i look at the, the i want that black wing. and ive considered the flat look too. only reason im leaning more toward the glossy look is because the wheels are glossy....