So, they sell matte blue and regular blued for my FP6...................................


how "matte" are we talking here? Anyone have pics?

I don't see a Matte blue FP6 extension.

Under magazine Extensions they list the FP6.
Under Matte blued extensions they only list Mossberg and Remington.

The last time I checked, Choate sold only a satin blue-black sulfate finish and a parkerized finish.
The sulfate blue was a close match for the older blued Remington Police guns.  

I'd recommend emailing Choate and asking what the story is.
They're good about fast responses, usually from a Choate family member.