Is is possible to change the home indicator color on an iPhone X? I mean the horizontal bar that suggest to slide from bottom to top to access the home screen.
No, it is not. The indicator will automatically adjust itself depending on what's below it, and it's not something you can directly control. As described in Designing for iPhone X, you generally don't want to do anything in your app specific to the home indicator (e.g. drawing any adornments).