Hi Colin,
Very similar to the mix I use, though after reading an SBS on painting uniforms in one of the magazines, I have changed the Dark Prussian Blue to Indigo (oils). It is not too different but I find the highlights come up a little more in keeping with the blue black overall feel of the material.
That said Dark Prussian Blue and Black (Vallejo acrylics) has worked well for you here.
Cheers,
Keith

The mix is about 3:1, Dark Prussian Blue:Black. I add more DPB and Sky Grey in incriments for highlights and add Black to the base for shadows. I found the DPB worked better than regular Prussian Blue as the PB is still too bright even with the black in the mix.
As stated, there was some trial and error in finding the colour but now I've batched a goodly amount as it worked for this fig, the 11th Light dragoon, the trousers of the Grenadier Guard and I think it would work for some French blues and ACW Union blue.

Handy mix

Just noticed your Toronto Cenataph avatar Colin - very apropos!

Colin

I used to go to that one every year but now I volunteer at the Sunnybrook Memorial, shuttling the Vets about the venue, to and from their rooms as well as setting up and tearing down the AV for the production.
They bring along of kids in from the surrounding neighbourhoods... this is so important that the younger generations aren't allowed to sweep our past under the rug.