The color change depends on how faded you have let the surface become before you treat. Technically, there are no shades of black but,,, I think, if you have a new vehicle, there wouldn't be any noticeable color change. But, if your vehicle is exposed to the sun and you treat it after six months, you will notice a color change particularly because not all of the plastic fades at the same rate. The differnce seems to be most noticable with the bumpers. Like I said in the first post, I treat all of the plastic, it seems to last for about six months and there is no noticable deterioration. This is in the Florida Keys where I have seen holes rot through the top of the fender flares on 4 year old DII's.
Some owners on this post have painted the flairs and bumper covers body color, in some colors that looks really good. Otherwise, do nothing and just replace the flairs after four years, they take about 15 minutes to snap off and on and only cost about $70.00 each. Over four years that might be less than the cost of treatment and the time involved.