I think it's the combination of dark green and blue-grey that kills it.
Here's another one - the Sunred Ford GT1 livery:
I understand that Sunred is a late entry and they only had enough time to prepare one car instead of two, so the livery probably isn't a priority. Nevertheless, it still looks horrible. It wouldn't be too bad if it was an orange car with black stripes, or a silver-white car with black stripes ... but the silver bonnet, orange body and the black wheel arches - especially that vertical line at the door - make it a real eyesore. Which is a shame, because it's a great-looking car.