People do black stone chip film in front of the rear wheel arch, black/carbon side scoop extensions, you could put black diffuser / side skirt / front splitter. The one that you may not remember I hate is the black obfuscation tape round the headlamp covers, I specifically got them to spray a yellow line round it instead.
I know the black accents can work, but I've thought long and hard about all these things and it's not for me. I think anything you can imagine being different I've probaby thought about and decided against. That's the joy of doing these kind of things, it's completely individual... I've just signed off the design of my customised seat pads!

Although they are not particularly interesting.