I was going to post this idea in the general discussion thread, but since you went with a diamond I'll try it here.
How about a different gemstone for each chip? Some ideas:
25c - White - Ivory or Quartz or Agate
1 - Blue - Sapphire or Opal
5 - Red - Ruby or Jasper
25 - Green - Emerald or Jade
100 - Black - Black Pearl or Obsidian (or Diamond?)
500 - Purple - Amethyst or Garnet
1000 - Yellow - Topaz
5000- Brown - Amber (or Gold?)
NCV - Orange-ish - Coral or ?????
Of course there are other possibilities; this
Wikipedia page has a good reference.
The Sapphire, Ruby, Emerald, Diamond, and Amethyst are traditionally considered the main "precious stones"; they could cover the 1 through the 500 if the diamond is used on the 100. I do kind of like the idea of a black pearl, though.
Anyway, just throwing the idea out there.