The King's Rangers crack reputation, ferocity, training, etc led to their being used as a "foundation unit" or template for both units of the Emperor's Lifeguards, and the Crown-guard of their home system, The Marches. These units are dressed and equipped in a manner reflecting their unique parentage, and the Rangers maintain a close relationship with both, even to being used to recruit and train prospective candidates.

Externally, the most obvious distinction between the three would be uniform colors - the King's Rangers normally wear gray-green, the Imperials wear Royal Blue, and the Crown-guard of The Marches wearing light blue-gray battledress.

Here, a slightly younger Cat, at this time a senior corporal in the Rangers, visits with a lance corporal of the Crown-guard, possibly during a training exercise.

Cat Scratch, King's Rangers, Crown-guard, etc {c} Me
Lance Corporal "Joe" of the Crown-guard {c} Teira {I asked her to name him because she made him the man he is today :D }
*Don't bother with the GIJoe jokes - i already went there...

Art and Lance-corporal Joe both by Teira at https://www.instagram.com/teira.artbook