This actually came up a few days ago - it depends on the car. The Ford GT will keep it's stripes - a C5 Z06 or Viper (of any vintage) won't. And the colour the stripes turn is also sort of tricky: I've painted a Ford GT both Taiga Metallic and Frash Green, fairly similar colours in game, but the former gave me white stripes, the latter, black.
Also, please try to use proper grammar / capitalization for future posts, as asked in the AUP you agreed to when joining. Welcome to the 'Planet!