What is the last number of the color lists in carcols.dat? Try add it after that and change #8 to the last number plus one. For example: last number of the color lists in carcols.dat is #255. Add it under #255 and change it to #256 (255 + 1 = 256).
Then, once you are done, change the number 8 that posted in color line, for example: fbi, x,8,x to fbi, x,256,x.
I've tried this method in GTA San Andreas and it works flawlessly.