Diamond-like Carbon (DLC) seems to be the most recent fad, and from what little bit I've read, I'm not totally sold on it. I'm guessing that's what they've left as samples.
Standard fare for a heatsink is to apply a dielectric coating to the mounting base (area of thermal conduction) and anodize for corrosion resistance. Then again, lots of companies simply mount with dielectric grease.
Another option for corrosion resistance might be Turcoat Accelagold, which carries a MIL spec rating as well. Many coating and anodizing outfits tend to carry this.