There is little, if any, GW fluff on Matorea. There is a wee bit from the madalfred site, but a darn little wee bit. I imagine it being founded by Imperials, and believe I have some written for it somewhere.
I purposefully used it as a location for a seafaring family associated with my Averland mercenary family, and having ties to Marienburg for commerce purposes as well. I picked the blue and orange because it seems to contrast well on the wheel of color, and it is totally different than any of the Imperial provinces.
Currently I only have a block of 20 maybe 25 swordsmen, and maybe 10 to 12 handgunners in line for my Matorean colors of orange and blue. I'd like to have some form of light cavalry, probably pistoliers at some point, but we'll see.
But I digress.
Main Imperial Province Tally 2018Averland ... GP
Hochland ... Gankom
Stirland ... Zygmund
Matorea ... Artobans