Balin is a significant member of Thorin's company, not least because he is eldest along with Thorin, is his second-in-command (as such), and develops respect for the outsider Bilbo more readily than his captain does. Balin's story continues between The Hobbit and The Lord of the Rings, and it's his fate we and his kinsman Gimli Gloinson discover in the Chambers of Marzabul. As Thorin's tale in The Hobbit speaks largely of the fall of many of his race, so does Balin's in the Mines of Moria.
Tolkien gives a little description of Balin - old, white-bearded, a red cloak, somewhat genial. Because of Balin's later significance as King of Khazad-Dum and his discovery of Durin's axe, I awarded him a nicer, more traditionally-Dwarven looking weapon among the figures, lengthening his beard with green stuff, and giving a lot of thought to his colour scheme, because let's face it: white beard + red cloak = Santa. Not good.
I'm going through John Rateliffe's superb exegesis Mr Baggins at the moment, and while its coverage of the individual Dwarves is as limited as it could be given their vagueness in Tolkien's novel, he does offer some helpful clues for broadening Balin visually. The most helpful is that Balin's beard and hair were initially golden - so a blonde base has been given to Balin's beard here. I've also paled up his complexion to further indicate his age; granted, it could go either way with that sort of thing, but I thought paler skin would look better against whitish hair.