RE datawindow colors: Can someone explain what the difference is between the transparent RGB color 553648127 (displays with a white "N" in the palette) and 536870912 (displays with a black "N" in the palette)?

In older versions of PB it was not possible to select the "black" one other than when the object was created. So we standardized on using the white "N". But now PB 2017 have changed that so even when you save a dw with the white "N" it switches to the black "N" color in most cases when you modify something unrelated on the datawindow. It is kind of annoying because it creates a bigger delta. But my main question is, why have two colors for the same thing? And what is the real difference?