I don't necessarily want to make them look more black. I want to make them easier to clean and keep them looking like the look now - new looking. My truck is only about 2 months old and I haven't gotten it really dirty yet so they look good but I can see over time, even with washing, they may fade or look dirty. I was hoping that keeping them coated with the undercarriage spray it would help keep them easier to clean and looking newer longer but I now see that the undercarriage spray may not be the best thing for those particular wheel well liners.