I do think the Ionelus family has some kind of sigil, since their personal funds are most likely seperate.
Just wanted to point out the Vallaki garda aren't typically trained professional soldiers for hire, but more like militia.
So they don't wear any colours, that is just the colour of the undyed leather, but brown is as good a guess as any.
Brown usually doesn't work too well for banners though, too muddy. But grey, white and blue would make sense.