Gänsewein (former)
Since the pontificate of Pope Benedict XVI (2005-2013) the Prefect of the Pontifical Household (formerly called the Majordomo of His Holiness) has been the Most Rev. Georg Gänswein, who also served Pope Benedict as his personal secretary. At the time Gänswein was ordained to the episcopacy he assumed a coat of arms that impaled (that is, combined side by side on the same shield) his own personal emblems with the coat of arms of the pope he served, Benedict XVI. Upon the abdication of of Pope Benedict and the election of Pope Francis Gänswein’s coat of arms changed to reflect the new pope he continued to serve as Prefect of the Pontifical Household. This is an old custom. Below are the coats of arms of several of these Prefects with their arms impaled with the various popes under whom they served.
Gänswein (current)
Harvey
Monduzzi
Martin
Nasalli Rocca di Corneliano
Callori di Vignale
EXARANDORUM 
I like the two first renditions 😉
I realize that when arms are impaled, the “color rule” is not quite as essential, but is there any way to separate the blue fields of both the personal arms of Gaenswein and of Francis for aesthetic reasons?
It’s true that the tincture rule doesn’t apply at all here. That rule concerns itself with the charges and field of a single coat of arms whereas impaled arms are two separate coats marshaled together on one shield. Sometimes that makes for less-than-happy combinations. Is there a way to separate them? Yes, the dividing line between them could be composed of a metal like gold or silver thus sharply dividing the two fields BUT that is an artistic, not a heraldic, decision. It could not, for example, be blazoned that way.
No, such a division between two fields with the same color is indeed not a heraldic ‘charge’. My solution (I always make gouaches) is: a sharp dividing-line with a pencil, then in the dexter half a tiny shadow-line by mixing blue: f.i. cobalt with ultramarine or ultramarine with prussian blue. then in the sinister half bright uplighting line by mixing blue with brighter blue or even a tip of white. I have the idea it works well. Then we get a suggestion of a tiny nick.