Looks like TW is going to win over a few celt fans with this post.
As a celt fan I hope the range of colors on the battlefield and in the towns isn't going to be all dirt tones. Celts used woad(?), had patterned clothing, and were ornately decorated in jewelry/gold. Being that this ties into the flair>effectiveness stance, I dont see why one wouldnt exploit this aspect of their culture. If the empire is has a cold steel aesthetic, the Battanians should be colorful and chaotic, with less need formation lines and less uniform soldier kits.