Is that from Hope's novels Orc, or your own preferred scheme? I need to go back to the books really - in my mind I have conflated too many of the details from Royal Flash with The Prisoner of Zenda and Rupert of Henzau! 
The only details I could find about uniforms in the books were:
1 - Rudolf wears a white uniform for his coronation;
2 - Police sergeants in Strelsau have a star on their collars and 'lace' on their cuffs (which I assume means some kind of braiding or frogging or something);
3 - recipients of the Order of the Rose (of Ruritania) get to wear red or red-and-yellow sashes.
I just went for a colour that a) wouldn't look Prussian; b) wouldn't look Austrian; c) wouldn't look Russian; and d) wouldn't be red (as I have Brits too). Doesn't leave a lot of choices!
Yellow seemed the obvious way to go - also, as one of my officers serves a dual role as my version of Colonel Sapt, Colonel Senf, and his English counterpart, Colonel Hammond-Mustard, it had to be 'mustard' jackets really...