Hmmm . . in the picture, it appears to me that, they are wearing the Leine. As for the "bright colored" outfits, this is historically accurate. The Celts used berries and plants to dye their wool clothing different colors. In the end, their clothing, once dyed, would look very much like a tartan.

The Celts' clothes showed their status and importance within the tribe. Men would wear a tunic with a belt, a cloak and trousers. Women wore dresses fastened with brooches.

In battle, the men in front would be nude and, the men in the rear would wear trousers and cloaks. Here is an account, from the Roman's point of views: http://www.isle-of-skye.org.uk/celti...ia/celt_c3.htm.