You have black, a sort of blue, and red accents.
There isn't really a province with blue and black as main colours, so I would look for a province with a combination of one of those with your red.
The new book states that most troopers wear 'some' piece of clothing in their provincial colours.
See page 36 - 2nd paragraph under the State Troops heading, and then there is a double page spread of uniform designs on pages 92-93.
The wording suggests that a trooper will wear some indication of his homeland - from doublet and hose or down to a mere ribbon or feather.
If you like the colour scheme you have chosen, and it would certainly stand out, then you could make them represent a town/area from a particular province, and 'one' of your chosen colours could be the link to the main province's colours.
So, for example, if you used the 'red' for your 'sign of allegiance' then you could choose Altdorf (where the sort of blue would tie in even better as already mentioned) or Talabecland, Ostermark, or Hochland.
If you went with the black, you have Nuln or say Averland.